#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll n;
string s[110];
int a[110][110];

bool cmp(string a, string b)
{
    return (a.size() < b.size());
}

int main(){
    ios_base::sync_with_stdio(0);
 cin.tie(0);
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> s[i];
    sort(s+1, s+n+1,cmp);
    for (int i = n; i; i--)
    {
        for (int j = 1; j < i; j++)
        {
            string rs = s[j], y;
            if (s[i].find(rs) == -1) continue;
            for (int z = 1; z < i; z++)
            {
                y = rs + s[z];
                if (s[i].find(y) == 0) rs = y, z = 0;
            }
            if (rs == s[i]) return cout << rs, 0;
        }
    }
    cout << -1;
}