sclass SimpleCircularBuffer<A> {
  A[] buffer;
  long base;
  int size;
  
  *(int capacity) {
    buffer = new A[capacity];
  }
  
  void add(A a) {
    if (size == buffer.length) {
      --size;
      ++base;
    }
    buffer[(int) ((base+size) % buffer.length)] = a;
    ++size;
  }
  
  A get(long pos) {
    if (pos < base || pos >= base+size) null;
    ret buffer[(int) ((pos-base) % buffer.length)];
  }
}