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

int main() {
    int N;
    cin >> N;
    priority_queue<deque<char>, vector<deque<char>>, greater<deque<char>>> pque;
    for (size_t i = 0; i < N; i++) {
        string S;
        cin >> S;
        deque<char> deq;
        for (size_t j = 0; j < S.size(); j++) {
            deq.push_back(S[j]);
        }
        pque.push(deq);
    }
    string ans = "";
    while (pque.size()) {
        auto deq = pque.top();
        pque.pop();
        ans += deq.front();
        deq.pop_front();
        if (deq.size()) {
            pque.push(deq);
        }
    }
    cout << ans << endl;
}