#include <iostream>
#include <queue>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
using namespace std;
template <class T> using reversed_priority_queue = priority_queue<T, vector<T>, greater<T> >;
int main() {
    int n; cin >> n;
    reversed_priority_queue<string> que;
    repeat (i,n) {
        string s; cin >> s;
        s += '\xff';
        que.push(s);
    }
    string ans = "";
    while (not que.empty()) {
        string t = que.top(); que.pop();
        ans += t[0];
        if (t.size() != 2) { // 1 is for the sentinel
            que.push(t.substr(1));
        }
    }
    cout << ans << endl;
    return 0;
}