#include <iostream>

using namespace std;

int main()
{
    int n;

    while (cin >> n, n)
    {
     int len = 10000;
     string str[10000];
     for (int i = 0; i < n; i ++ )
     {
     cin >> str[i];
     if (len > str[i].size()) len = str[i].size();
     }
     while (len)
        {
            bool success = true;
            for (int i = 1; i < n; i ++ )
            {
                bool is_same = true;
                for (int j = 1; j <= len; j ++ )
                if (str[0][str[0].size() - j] != str[i][str[i].size() - j])
                    {
                        is_same = false;
                        break;
                    }
                if (!is_same)
                    {
                        success = false;
                        break;
                    }

            }
            if (success) break;
            len --;
        }
            cout << str[0].substr(str[0].size() - len) << endl;
    }
    return 0;
}