#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = a; i < b; i++)
using ll = long long;

int main(){
    int n, x;
    string s;
    char c;
    cin >> n >> s >> x >> c;
    s[x - 1] = c;
    cout << s << endl;
}