#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());
}

void poz(int x, int y)
{
    string c = s[x], S = s[y];
    int i = 0, j = 0;
    while (i < S.size())
    {
        j = 0;bool u = 0;
        while (S[i] == c[j] && j < c.size() && i < S.size()) i++, j++, u = 1;
        if (j == c.size()) a[x][y] += c.size();
        if (u) continue;
        else i++;
    }
}

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) != -1) rs = y, z = 0;
            }
            if (rs == s[i]) return cout << rs, 0;
        }
    }
    cout << -1;
}