#include <iostream>
#include <stdio.h>
#include <fstream>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <limits.h>
#include <math.h>
#include <functional>
#include <bitset>
#include <iomanip>

#define repeat(i,n) for (long long i = 0; (i) < (n); ++ (i))
#define debug(x) cerr << #x << ": " << x << '\n'
#define debugArray(x,n) for(long long i = 0; (i) < (n); ++ (i)) cerr << #x << "[" << i << "]: " << x[i] << '\n'
#define debugArrayP(x,n) for(long long i = 0; (i) < (n); ++ (i)) cerr << #x << "[" << i << "]: " << x[i].first<< " " << x[i].second << '\n'

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> Pii;
typedef vector<int> vint;
typedef vector<ll> vll;
const ll INF = INT_MAX;
const ll MOD = 1e9+7;


int main(){
  int N;cin>>N;
  vector<string> S(N);
  repeat(i,N){
    cin>>S[i];
    for(int j=S[i].length();j<51;j++){
      S[i] += 'z'+1;
    }
  }
  string ans;
  while(!S.empty()){
    sort(S.begin(),S.end());
    ans += S[0][0];
    S[0].erase(S[0].begin());
    if(S[0][0]=='z'+1)S.erase(S.begin());
  }
  cout << ans << endl;
  return 0;
}