#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;

int main() {
    priority_queue<deque<char>, vector<deque<char>>, greater<deque<char>>> que;
    int n;
    cin >> n;
    string ret = "";
    for (int i = 0; i < n; i++) {
        string s;
        cin >> s;
        deque<char> deq;
        for (char c: s) {
            deq.push_back(c);
        }
        que.push(deq);
    }

    while (que.size()) {
        ret += que.top().front();
        auto t = que.top();
        que.pop();
        t.pop_front();
        if (t.size()) {
            que.push(t);
        }
    }
    cout << ret << endl;
}