#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)n; i++)

int main() {
  int N;
  cin >> N;
  vector<vector<int>> S(N, vector<int> (26, 0));
  rep(i, N) {
    string Si;
    cin >> Si;
    for (char c : Si)
      S[i][c - 'a']++;
  }
  vector<vector<int>> T(N*26, vector<int> (26));
  rep(i, N) {
    vector<int> tmp = S[i];
    rep(j, 26) {
      tmp[j]++;
      T[i*26+j] = tmp;
      tmp[j]--;
    }
  }
  auto prt = [&](vector<int> v) {
    rep(i, 26)
      rep(j, v[i]) cout << char(int('a') + i);
    return;
  };
  rep(i, N*26) {
    int cnt = 0;
    rep(j, N*26) {
      if (T[i] == T[j])
	cnt++;
    }
    if (cnt == 1) {
      prt(T[i]); cout << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}