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;
string s[100005];
string ans;
int n, v['z' + 5], h['z' + 5], pos = 1, g['z' + 5], t['z' + 5];
void DFS(int nod) {
  if (v[nod]) {
    pos = 0;
    return;
  }
  v[nod] = 1;
  ans += (char)nod;
  if (t[nod]) DFS(t[nod]);
}
int32_t main() {
  ios_base ::sync_with_stdio(0);
  cin.tie();
  cout.tie();
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> s[i];
    for (int j = 'a'; j <= 'z'; j++) v[j] = 0;
    for (int j = 0; j < s[i].length(); j++) {
      if (v[s[i][j]]) {
        cout << "NO";
        return 0;
      }
      v[s[i][j]] = 1;
      if (j != 0) {
        if (g[s[i][j]]) {
          if (g[s[i][j]] != s[i][j - 1]) {
            cout << "NO";
            return 0;
          }
        } else {
          g[s[i][j]] = s[i][j - 1];
        }
        if (t[s[i][j - 1]]) {
          if (t[s[i][j - 1]] != s[i][j]) {
            cout << "NO";
            return 0;
          }
        } else {
          t[s[i][j - 1]] = s[i][j];
        }
      }
      h[s[i][j]] = 1;
    }
  }
  for (int j = 'a'; j <= 'z'; j++) v[j] = 0;
  for (int i = 'a'; i <= 'z'; i++) {
    if (!h[i])
      v[i] = 1;
    else if (!v[i] && !g[i])
      DFS(i);
  }
  for (int i = 'a'; i <= 'z'; i++) {
    if (!v[i]) {
      cout << "NO";
      return 0;
    }
  }
  if (pos)
    cout << ans;
  else
    cout << "NO";
}
