#include <bits/stdc++.h>
#include<atcoder/all>
using namespace atcoder;
using namespace std;
using ll=long long;
using ld=long double;
ll mod=998244353;
ll inf=1000000000000000000;
int main(){
    ll n;
    cin >> n;
    vector<string>s(n);
    for (ll i = 0; i < n; i++)
    {
        cin >> s[i];
        sort(s[i].begin(),s[i].end());
    }
    for (ll i = 0; i < n; i++)
    {
        map<char,ll>memo,memo2;
        for (ll j = 0; j < s[i].size(); j++)
        {
            memo2[s[i][j]]++;
        }
        bool ok=true;
        for (ll j = 0; j < n; j++)
        {
            if (j==i)
            {
                continue;
            }
            memo=memo2;
            bool o=true;
            for (ll k = 0; k < s[j].size(); k++)
            {
                if (memo[s[j][k]]==0)
                {
                    o=false;
                    break;
                }else{
                    memo[s[j][k]]--;
                }
            }
            if (o)
            {
                ok=false;
                break;
            }
            
        }
        if (ok)
        {
            cout << s[i] << endl;
            return 0;
        }
    }
    cout << -1 << endl;
}