#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']++;
  }
  rep(i, N) {
    int ap = -1;
    string T;
    rep(j, N) {
      if (i == j)
	continue;
      int dif = 0;
      T = "";
      int is = 0, js = 0;
      rep(k, 26) {
	rep(l, S[i][k])
	  T += char(int('a') + k);
	is += S[i][k];
	js += S[j][k];
	dif += abs(S[i][k] - S[j][k]);
	if (ap < 0 && S[i][k] == 0 && S[j][k] == 0)
	  ap = k;
      }
      if (is == js && dif <= 1) {
	ap = -1;
	break;
      }
    }
    if (ap < 0)
      continue;
    cout << T << char(int('a') + ap) << endl;
    return 0;
  }
  cout << -1 << endl;
  return 0;
}