asclass CompactAbstractMap<K, V> implements Map<K, V> {
  public int size() {
      return entrySet().size();
  }

  public boolean isEmpty() {
      return size() == 0;
  }

  public boolean containsValue(Object value) {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      if (value == null) {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (e.getValue() == null)
                  return true;
          }
      } else {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (value.equals(e.getValue()))
                  return true;
          }
      }
      return false;
  }

  public boolean containsKey(Object key) {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      if (key == null) {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (e.getKey() == null)
                  return true;
          }
      } else {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (key.equals(e.getKey()))
                  return true;
          }
      }
      return false;
  }

  public V get(Object key) {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      if (key == null) {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (e.getKey() == null)
                  return e.getValue();
          }
      } else {
          while (i.hasNext()) {
              Entry<K, V> e = i.next();
              if (key.equals(e.getKey()))
                  return e.getValue();
          }
      }
      return null;
  }

  public V put(K key, V value) {
      throw new UnsupportedOperationException();
  }

  public V remove(Object key) {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      Entry<K, V> correctEntry = null;
      if (key == null) {
          while (correctEntry == null && i.hasNext()) {
              Entry<K, V> e = i.next();
              if (e.getKey() == null)
                  correctEntry = e;
          }
      } else {
          while (correctEntry == null && i.hasNext()) {
              Entry<K, V> e = i.next();
              if (key.equals(e.getKey()))
                  correctEntry = e;
          }
      }

      V oldValue = null;
      if (correctEntry != null) {
          oldValue = correctEntry.getValue();
          i.remove();
      }
      return oldValue;
  }

  public void putAll(Map<? extends K, ? extends V> m) {
      for (Entry<? extends K, ? extends V> e : m.entrySet())
          put(e.getKey(), e.getValue());
  }

  public void clear() {
      entrySet().clear();
  }

  public Set<K> keySet() {
      return new AbstractSet<K>() {
          public Iterator<K> iterator() {
              return new Iterator<K>() {
                  private Iterator<Entry<K, V>> i = entrySet().iterator();

                  public boolean hasNext() {
                      return i.hasNext();
                  }

                  public K next() {
                      return i.next().getKey();
                  }

                  public void remove() {
                      i.remove();
                  }
              };
          }

          public int size() {
              return CompactAbstractMap.this.size();
          }

          public boolean isEmpty() {
              return CompactAbstractMap.this.isEmpty();
          }

          public void clear() {
              CompactAbstractMap.this.clear();
          }

          public boolean contains(Object k) {
              return CompactAbstractMap.this.containsKey(k);
          }
      };
  }

  public Collection<V> values() {
      return new AbstractCollection<V>() {
          public Iterator<V> iterator() {
              return new Iterator<V>() {
                  private Iterator<Entry<K, V>> i = entrySet().iterator();

                  public boolean hasNext() {
                      return i.hasNext();
                  }

                  public V next() {
                      return i.next().getValue();
                  }

                  public void remove() {
                      i.remove();
                  }
              };
          }

          public int size() {
              return CompactAbstractMap.this.size();
          }

          public boolean isEmpty() {
              return CompactAbstractMap.this.isEmpty();
          }

          public void clear() {
              CompactAbstractMap.this.clear();
          }

          public boolean contains(Object v) {
              return CompactAbstractMap.this.containsValue(v);
          }
      };
  }

  public abstract Set<Entry<K, V>> entrySet();

  public boolean equals(Object o) {
      if (o == this)
          return true;

      if (!(o instanceof Map))
          return false;
      Map<?, ?> m = (Map<?, ?>) o;
      if (m.size() != size())
          return false;

      try {
          for (Entry<K, V> e : entrySet()) {
              K key = e.getKey();
              V value = e.getValue();
              if (value == null) {
                  if (!(m.get(key) == null && m.containsKey(key)))
                      return false;
              } else {
                  if (!value.equals(m.get(key)))
                      return false;
              }
          }
      } catch (ClassCastException unused) {
          return false;
      } catch (NullPointerException unused) {
          return false;
      }

      return true;
  }

  public int hashCode() {
      int h = 0;
      for (Entry<K, V> entry : entrySet())
          h += entry.hashCode();
      return h;
  }

  public String toString() {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      if (!i.hasNext())
          return "{}";

      StringBuilder sb = new StringBuilder();
      sb.append('{');
      for (; ; ) {
          Entry<K, V> e = i.next();
          K key = e.getKey();
          V value = e.getValue();
          sb.append(key == this ? "(this Map)" : key);
          sb.append('=');
          sb.append(value == this ? "(this Map)" : value);
          if (!i.hasNext())
              return sb.append('}').toString();
          sb.append(',').append(' ');
      }
  }

  protected Object clone() throws CloneNotSupportedException {
      CompactAbstractMap<?, ?> result = (CompactAbstractMap<?, ?>) super.clone();
      return result;
  }

  public static class SimpleEntry<K, V>
          implements Entry<K, V>, java.io.Serializable {
      @java.io.Serial
      private static final long serialVersionUID = -8499721149061103585L;

      @SuppressWarnings("serial")
      private final K key;
      @SuppressWarnings("serial")
      private V value;

      public SimpleEntry(K key, V value) {
          this.key = key;
          this.value = value;
      }

      public SimpleEntry(Entry<? extends K, ? extends V> entry) {
          this.key = entry.getKey();
          this.value = entry.getValue();
      }

      public K getKey() {
          return key;
      }

      public V getValue() {
          return value;
      }

      public V setValue(V value) {
          V oldValue = this.value;
          this.value = value;
          return oldValue;
      }

      public boolean equals(Object o) {
          if (!(o instanceof Map.Entry))
              return false;
          Entry<?, ?> e = (Entry<?, ?>) o;
          return eq(key, e.getKey()) && eq(value, e.getValue());
      }

      public int hashCode() {
          return (key == null ? 0 : key.hashCode()) ^
                  (value == null ? 0 : value.hashCode());
      }

      public String toString() {
          return key + "=" + value;
      }

  }

  public static class SimpleImmutableEntry<K, V>
          implements Entry<K, V>, java.io.Serializable {
      @java.io.Serial
      private static final long serialVersionUID = 7138329143949025153L;

      @SuppressWarnings("serial")
      private final K key;
      @SuppressWarnings("serial")
      private final V value;

      public SimpleImmutableEntry(K key, V value) {
          this.key = key;
          this.value = value;
      }

      public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
          this.key = entry.getKey();
          this.value = entry.getValue();
      }

      public K getKey() {
          return key;
      }

      public V getValue() {
          return value;
      }

      public V setValue(V value) {
          throw new UnsupportedOperationException();
      }

      public boolean equals(Object o) {
          if (!(o instanceof Map.Entry))
              return false;
          Entry<?, ?> e = (Entry<?, ?>) o;
          return eq(key, e.getKey()) && eq(value, e.getValue());
      }

      public int hashCode() {
          return (key == null ? 0 : key.hashCode()) ^
                  (value == null ? 0 : value.hashCode());
      }

      public String toString() {
          return key + "=" + value;
      }
  }
}