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

int main(){
	string s;
	int n1;
	char a[50]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x'};
	cin>>n1>>s;
	for(int i=0;i<s.size();i++){
		i+=n1;
		cout<<a[i];
	}
	return 0;
}