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

int solve(void) {
	int K;
	cin >> K;
	string S;
	cin >> S;
	int N = S.size();
	
	for(int i = 0; i < N; ++i) {
		if(i < K) cout << S[0];
		else cout << S[i - K];
	}
	cout << "\n";
	
	return 0;
}

int main(void) {
	int T;
	cin >> T;
	
	while(T--) solve();
	
	return 0;
}