import java.util.*;
import java.util.zip.*;
import java.util.List;
import java.util.regex.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
import javax.swing.table.*;
import java.io.*;
import java.net.*;
import java.lang.reflect.*;
import java.lang.ref.*;
import java.lang.management.*;
import java.security.*;
import java.security.spec.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.imageio.*;
import java.math.*;
class main {

static String replaceOneCharInString(String a, int idx, String b) {
  return spliceString(a, idx, idx+1, b);
}

static String replaceOneCharInString(String a, int idx, char b) {
  return replaceOneCharInString(a, idx, str(b));
}
static String spliceString(String a, int from, int to, String b) {
  return substring(a, 0, from) + b + substring(a, Math.max(from, to));
}

static String spliceString(String a, int from, int to, char b) {
  return spliceString(a, from, to, str(b));
}

static String str(Object o) {
  return o == null ? "null" : o.toString();
}

static String str(char[] c) {
  return new String(c);
}



static String substring(String s, int x) {
  return substring(s, x, strL(s));
}

static String substring(String s, int x, int y) {
  if (s == null) return null;
  if (x < 0) x = 0;
  int n = s.length();
  if (y < x) y = x;
  if (y > n) y = n;
  if (x >= y) return "";
  return s.substring(x, y);
}



// convenience method for quickly dropping a prefix
static String substring(String s, CharSequence l) {
  return substring(s, lCharSequence(l));
}



static int strL(String s) {
  return s == null ? 0 : s.length();
}

static int lCharSequence(CharSequence s) {
  return s == null ? 0 : s.length();
}


}