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

#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define rep2(i, j, n) for (int i = (int)j; i < (int)n; i++)
using pii = pair<int, int>;

bool comp(pii a, pii b) {
  if (a.first != b.first)
    return a.first > b.first;
  else
    return a.second < b.second;
}

int main() {
  int N;
  cin >> N;
  vector<vector<int>> S(N, vector<int> (26, 0));
  vector<pii> sv(N);
  rep(i, N) {
    string Si;
    cin >> Si;
    for (char c : Si)
      S[i][c - 'a']++;
    sv.push_back({(int)Si.size(), i});
  }
  sort(sv.begin(), sv.end(), comp);
  if (sv[0].first != sv[1].first) {
    int a = 0;
    rep(i, 26) {
      if (S[sv[0].second][i] == 0)
	a = i;
      rep(j, S[sv[0].second][i])
	cout << char(int('a')+i);
    }
    cout << char(int('a')+a) << endl;
  } else {
    int a = 0;
    int dif = 0;
    rep(i, 26) {
      if (S[sv[0].second][i] != S[sv[1].second][i])
	dif++;
      if (S[sv[1].second][i] == 0)
	a = i;
    }
    if (dif == 0) cout << -1 << endl;
    else {
      rep(i, 26) {
	rep(j, S[sv[0].second][i])
	  cout << char(int('a')+i);
      }
      cout << char(int('a')+a) << endl;
    }
  }
  return 0;
}