#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

bool check(vector<int> a, vector<int> b) {
    assert(a.size() == b.size() && a.size() == 26);
    int cnt = 0;
    for (int i = 0; i < 26; i++) {
        if (a[i] < b[i] || a[i] > b[i] + 1) {
            return false;
        }
        if (a[i] != b[i]) {
            cnt++;
        }
    }
    return cnt == 1;
}
int main() {
    fast_io();
    int n;
    cin >> n;
    vector<string> s(n);
    for (int i = 0; i < n; i++) {
        cin >> s[i];
    }
    vector<vector<int>> cnt(n, vector<int>(26));
    for (int i = 0; i < n; i++) {
        for (char c : s[i]) {
            cnt[i][c - 'a']++;
        }
    }
    for (int i = 0; i < n; i++) {
        for (int c = 0; c < 26; c++) {
            cnt[i][c]++;
            bool is_ok = true;
            for (int j = 0; j < n; j++) {
                if (i == j) {
                    continue;
                }
                if (check(cnt[i], cnt[j])) {
                    is_ok = false;
                    break;
                }
            }
            if (is_ok) {
                for (int k = 0; k < 26; k++) {
                    for (int l = 0; l < cnt[i][k]; l++) {
                        cout << (char)('a' + k);
                    }
                }
                cout << endl;
                return 0;
            }
            cnt[i][c]--;
        }
    }
    cout << "-1" << endl;
}