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

int main() {
    int N;
    cin >> N;
    priority_queue<string, vector<string>, greater<>> que;
    for (int i = 0; i < N; i++) {
        string S;
        cin >> S;
        S += 'z' + 1;
        que.push(S);
    }

    string ans;
    while (!que.empty()) {
        string S = que.top();
        que.pop();
        ans += S[0];
        if (S.length() >= 3)
            que.push(S.substr(1));
    }

    cout << ans << endl;
}