/* -*- coding: utf-8 -*-
 *
 * 2715.cc:  No.2715 Unique Chimatagram - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_N = 1000;
const int MAX_L = 10;

/* typedef */

/* global variables */

int cs[MAX_N][26], ls[MAX_N];

/* subroutines */

int anagram(char s[], int cs[]) {
  int l = 0;
  for (int i = 0; s[i]; i++) cs[s[i] - 'a']++, l++;
  return l;
}

bool chimata(int i, int j) {
  bool f = true;
  if (ls[i] != ls[j] + 1) f = false;
  else {
    int k1 = 0;
    for (int a = 0; f && a < 26; a++) {
      if (cs[i][a] == cs[j][a] + 1) k1++;
      else if (cs[i][a] != cs[j][a]) f = false;
    }
    f = (f && (k1 == 1));
  }
  //printf(" chimate(%d,%d)=%d\n", i, j, f);
  return f;
}

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (int i = 0; i < n; i++) {
    char s[MAX_L + 4];
    scanf("%s", s);
    ls[i] = anagram(s, cs[i]);
  }

  for (int i = 0; i < n; i++)
    for (int a = 0; a < 26; a++) {
      cs[i][a]++, ls[i]++;

      bool ok = false;
      for (int j = 0; ! ok && j < n; j++)
	if (i != j) ok = chimata(i, j);

      if (! ok) {
	for (int k = 0; k < 26; k++)
	  for (int c = 0; c < cs[i][k]; c++) putchar('a' + k);
	putchar('\n');
	return 0;
      }
      
      cs[i][a]--, ls[i]--;
    }

  puts("-1");
  return 0;
}