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

void solve(){
  int k;
  string s;
  cin>>k>>s;
  int n=s.size();
  k=min(k,n);
  string ans=string(k,s[0])+s.substr(0,n-k);
  cout<<ans<<endl;
}

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