#include <iostream>

using namespace std;

int const N = 200;

int n;
string str[N];

int main() {
    while (cin >> n, n) {
        int len = 1000;
        for (int i = 0; i < n; i++) {
            cin >> str[i];
            if (str[i].size() < len) len = str[i].size();
        }

        string a, b, c;

        while (len) {
            for (int j = 1; j < n; j++) {
                    a = str[0].substr(str[0].size() - len);
                    b = str[j].substr(str[j].size() - len);

                    // cout << a << endl;
                    // cout << b << endl;
                    if (a != b) {
                        len--;
                        break;
                    }
                    if (a == b && j == n - 1) {
                        c = a;
                        len = 0;
                        break;
                    }
            }
        }
        cout << c << endl;
    }
    return 0;
}