#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) {
    vector<int> si = S[i];
    rep(ii, 26) {
      si[ii] += 1;
      bool jud = true;
      rep(j, N) {
	if (i == j)
	  continue;
	vector<int> sj = S[j];
	rep(jj, 26) {
	  sj[jj] += 1;
	  if (si == sj) {
	    jud =false;
	  }
	  sj[jj] -= 1;
	}
      }
      if (jud) {
	rep(k, 26)
	  rep(k2, si[k])
	  cout << char(int('a') + k);
	cout << endl;
	return 0;
      }
      si[ii] -= 1;
    }
  }
  cout << -1 << endl;
  return 0;
}