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, ne[200005], fr[26], pr[26];
int vis[26];
bool over[26];
int fl;
string s;
set<string> se;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  memset(ne, -1, sizeof(ne));
  memset(pr, -1, sizeof(pr));
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s;
    memset(fr, 0, sizeof(fr));
    for (int j = 0; j < s.length(); j++) {
      if (fr[s[j] - 'a']) {
        cout << "NO";
        return 0;
      }
      fr[s[j] - 'a']++;
      vis[s[j] - 'a'] = 1;
      if (j && ne[s[j - 1] - 'a'] == -1) ne[s[j - 1] - 'a'] = s[j] - 'a';
      if (j && ne[s[j - 1] - 'a'] != s[j] - 'a') {
        cout << "NO";
        return 0;
      }
      if (j && pr[s[j] - 'a'] == -1) pr[s[j] - 'a'] = s[j - 1] - 'a';
      if (j && pr[s[j] - 'a'] != s[j - 1] - 'a') {
        cout << "NO";
        return 0;
      }
    }
  }
  string ans = "";
  for (int i = 0; i < 26; i++) {
    if (over[i] || !vis[i] || pr[i] != -1) continue;
    int cur = i;
    ans = "";
    while (cur != -1) {
      if (over[cur] || !vis[cur]) {
        cout << "NO h";
        return 0;
      }
      over[cur] = 1;
      ans += 'a' + cur;
      cur = ne[cur];
    }
    se.insert(ans);
  }
  for (int i = 0; i < 26; i++) {
    if (vis[i] && over[i]) continue;
    if (vis[i] || over[i]) {
      cout << "NO";
      return 0;
    }
  }
  for (auto ans : se) cout << ans;
  return 0;
}
