#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

const int N = 1010;
const int L = 45;
char a[N][L];
char s[L];
int b[L];
int n, m;

bool check()
{
    for (int i = 0; i < n; i++)
    {
        int cnt = 0;
        for (int j = 0; j < m; j++)
            cnt += (int)(s[j] != a[i][j]);
        if (cnt >= 2) return false;
    }
    return true;
}

int main()
{
    scanf("%d", &n);
    for (int i = 0; i < n; i++)
        scanf(" %s ", a[i]);
    m = strlen(a[0]);
    s[m] = (char)0;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
        {
            if (a[i][j] == s[j] || b[j] == 0)
            {
                s[j] = a[i][j];
                b[j]++;
            }
            else
                b[j]--;
        }
    for (int i = 0; i < n; i++)
    {
        int cnt = 0;
        for (int j = 0; j < m; j++)
            cnt += (int)(s[j] != a[i][j]);
        if (cnt <= 1) continue;
        if (cnt != 2) throw;
        for (int j = 0; j < m; j++)
        {
            if (s[j] == a[i][j]) continue;
            char old = s[j];
            s[j] = a[i][j];
            if (check())
            {
                printf("%s\n", s);
                return 0;
            }
            s[j] = old;
        }
        throw;
    }
    printf("%s\n", s);

    return 0;
}