#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>
#include <deque>

using namespace std;

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

typedef long long ll;

int main() {

  int N; cin >> N;
  deque<string> vec(N);
  rep(i, N) {
    cin >> vec[i];
  }

  std::string ans;
  while(!vec.empty()) {
    stable_sort(vec.begin(), vec.end());
    ans += vec[0][0];
    vec[0] = vec[0].substr(1);
    if(vec[0].empty()) { vec.pop_front(); }
  }

  cout << ans << endl;

  return 0;
}