#include <bits/stdc++.h>
using namespace std;
#define test int t; cin>>t; while (t--)
#define ll long long int
#define fellow_junior  ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int main()
{
   fellow_junior
   int t,i,j;
   while(cin>>t && t)
   {
       map<string,int>a;
       string x;
       for(i=0;i<t;i++)
       {
           cin>>x;
           a[x]++;
       }
       for(i=0;i<t;i++)
       {
           cout<<a[i].first;
       }
       cout<<endl;
   }
   return 0;
}