#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    int n, x;
    string s;
    char c;
    cin >> n >> s >> x >> c;
    x--;
    s[x] = c;
    cout << s << endl;
    return 0;
}