#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
    int n;
    while (cin >> n, n)
    {
        string strs[n];
        int min_len = 210;
        for (int i = 0; i < n; i ++) 
        {
            string s;
            cin >> s;
            reverse(s.begin(), s.end());
            min_len = min(min_len, (int)s.size());
            strs[i] = s;
        }

        string res;
        for (int i = 0; i < min_len; i ++)
        {
            char c = strs[0][i];
            bool flag = true;
            for (string s : strs)
                if (s[i] != c)
                {
                    flag = false;
                    break;
                }
            if (flag) res += c;
            else break;
        }
        reverse(res.begin(), res.end());
        cout << res << endl;
    }

    return 0;
}