#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::cout.tie(nullptr);
	srand((unsigned)time(NULL));
	int n,x;
	string s;
	char c;
	cin>>n>>s>>x>>c;
	s[x-1] = c;
	cout<<s<<endl;
}