#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  priority_queue<string, vector<string>, greater<string> > Q;
  string ret;

  int n;
  cin >> n;
  REP (i, n) {
    string s;
    cin >> s;
    Q.push(s + "|");
  }

  while (!Q.empty()) {
    string x = Q.top();
    Q.pop();
    ret += x[0];
    x = x.substr(1);
    if (x != "|")
      Q.push(x);
  }
  
  cout << ret << endl;
  
  return 0;
}