/* -*- coding: utf-8 -*-
 *
 * 3610.cc:  No.3610 CHANGE - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 100;

/* typedef */

/* global variables */

char s[MAX_N + 4];

/* subroutines */

/* main */

int main() {
  int n, x;
  char cs[4];
  scanf("%d%s%d%s", &n, s, &x, cs);

  s[x - 1] = cs[0];
  puts(s);
  
  return 0;
}