A substring of some string is called the most frequent, if the number of its occurrences is not less than number of occurrences of any other substring.

You are given a set of strings. A string (not necessarily from this set) is called good if all elements of the set are the most frequent substrings of this string. Restore the non-empty good string with minimum length. If several such strings exist, restore lexicographically minimum string. If there are no good strings, print "NO" (without quotes).

A substring of a string is a contiguous subsequence of letters in the string. For example, "ab", "c", "abc" are substrings of string "abc", while "ac" is not a substring of that string.

The number of occurrences of a substring in a string is the number of starting positions in the string where the substring occurs. These occurrences could overlap.

String a is lexicographically smaller than string b, if a is a prefix of b, or a has a smaller letter at the first position where a and b differ.

Input

The first line contains integer n (1 ≤ n ≤ 105) — the number of strings in the set.

Each of the next n lines contains a non-empty string consisting of lowercase English letters. It is guaranteed that the strings are distinct.

The total length of the strings doesn't exceed 105.

Output

Print the non-empty good string with minimum length. If several good strings exist, print lexicographically minimum among them. Print "NO" (without quotes) if there are no good strings.

Examples

Input

4
mail
ai
lru
cf


Output

cfmailru


Input

3
kek
preceq
cheburek


Output

NO

Note

One can show that in the first sample only two good strings with minimum length exist: "cfmailru" and "mailrucf". The first string is lexicographically minimum.
#include <bits/stdc++.h>
using namespace std;
int n, m, len;
char buf[233333];
int pre[233], nex[233];
int f[26], ff[26];
int main() {
  memset(pre, -1, sizeof(pre));
  memset(nex, -1, sizeof(nex));
  scanf("%d", &n);
  for (int t = 1; t <= n; t++) {
    scanf(" %s", buf);
    len = strlen(buf);
    memset(f, 0, sizeof(f));
    for (int i = 0; i < len; i++) {
      if (f[buf[i] - 'a']) {
        printf("NO\n");
        return 0;
      }
      f[buf[i] - 'a'] = 1;
      ff[buf[i] - 'a'] = 1;
    }
    for (int i = 1; i < len; i++) {
      if (pre[buf[i] - 'a'] != -1 && pre[buf[i] - 'a'] != buf[i - 1] - 'a') {
        printf("NO\n");
        return 0;
      }
      pre[buf[i] - 'a'] = buf[i - 1] - 'a';
      if (nex[buf[i - 1] - 'a'] != -1 &&
          nex[buf[i - 1] - 'a'] != buf[i] - 'a') {
        printf("NO\n");
        return 0;
      }
      nex[buf[i - 1] - 'a'] = buf[i] - 'a';
    }
  }
  int cnt = 0, cnt2 = 0;
  for (int i = 0; i < 26; i++) {
    if (ff[i]) {
      cnt++;
      if (pre[i] == -1) {
        for (int j = i; j != -1; j = nex[j]) {
          cnt2++;
        }
      }
    }
  }
  if (cnt != cnt2) {
    printf("NO\n");
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    if (ff[i]) {
      if (pre[i] == -1) {
        for (int j = i; j != -1; j = nex[j]) {
          printf("%c", j + 'a');
        }
      }
    }
  }
  printf("\n");
  return 0;
}
