#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int main(){
	ll n,x;
	string s,c;
	cin>>n>>s>>x>>c;
	for(int i=0;i<n;i++){
		if(i==x-1){
			cout<<c;
		}
		else{
			cout<<s[i];
		}
	}
}