#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define fr(i, a, b) for (int i = (a); i < (b); i++)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int N;
int p[50];
string S[50];

int main() {
    cin >> N;

    rep (i, N) {
        cin >> S[i];
        S[i] += '~';
    }

    string T;

    for (;;) {
        char c = '~';
        int id = 0;

        for (int i = 0; i < N; i++) {
            if (c > S[i][p[i]]) {
                c = S[i][p[i]];
                id = i;
            }
        }


        if (c == '~') break;
        T += S[id][p[id]++];
    }

    cout << T << endl;
}