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>
#pragma GCC optimize("Ofast")
using namespace std;
bool use[100];
signed main() {
  int n;
  scanf("%d", &n);
  bool joke = true;
  map<char, char> nxt, lst;
  for (int i = 0; i < 26; ++i) {
    char c = 'a' + i;
    nxt[c] = lst[c] = '.';
  }
  for (int it = 0; it < n; ++it) {
    string s;
    cin >> s;
    int sz = (int)s.size();
    for (auto c : s) {
      use[c - 'a'] = true;
    }
    for (int i = 0; i < sz - 1; ++i) {
      if (nxt[s[i]] == '.') {
        nxt[s[i]] = s[i + 1];
      } else if (nxt[s[i]] == s[i + 1]) {
        ;
      } else {
        joke = false;
        break;
      }
      if (lst[s[i + 1]] == '.') {
        lst[s[i + 1]] = s[i];
      } else if (lst[s[i + 1]] == s[i]) {
        ;
      } else {
        joke = false;
        break;
      }
    }
  }
  for (int i = 0; i < 26; ++i) {
    if (!joke) break;
    char c = 'a' + i;
    vector<bool> used(26);
    while (c != '.') {
      if (used[c - 'a']) {
        joke = false;
        break;
      }
      used[c - 'a'] = true;
      c = nxt[c];
    }
  }
  if (!joke) {
    puts("NO");
    return 0;
  }
  for (int i = 0; i < 26; ++i) {
    char c = 'a' + i;
    if (lst[c] == '.' && use[i]) {
      while (c != '.') {
        cout << c;
        c = nxt[c];
      }
    }
  }
  cout << "\n";
  return 0;
}
