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

int main() {
	int a, b;
	cin >> a;
	string S;
	cin >> S;
	char s;
	cin >> b >> s;
	b--;
	for (int i = 0; i < a; i++) {
		if (i == b) cout << s;
		else cout << S[i];
	}
	cout << endl;
}