#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;

void solve() {
    int k;
    string s;
    cin >> k >> s;
    int n = s.size();
    
    if (k >= n) {
        cout << string(n, s[0]) << '\n';
        return;
    }
    
    string ans(n, '.');
    rep(i, k) ans[i] = s[0];
    for (int i = k; i < n; ++i) ans[i] = s[i-k];
    
    cout << ans << '\n';
}

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