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

using namespace std;

template<typename T> using pq = priority_queue<T, vector<T>, greater<T>>;

int main(){
    
    int N;
    cin >> N;
    string T="", S;
    pq<string> que;
    for (int i=0; i<N; i++){
        cin >> S;
        S += "{";
        que.push(S);
    }

    while(!que.empty()){
        S = que.top();
        que.pop();
        T += S[0];
        if (S.size() > 2){
            S = S.substr(1);
            que.push(S);
        }
    }

    cout << T << endl;

    return 0;
}