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;
bool mainHook() {
  int n;
  cin >> n;
  vector<vector<char> > mat(26, vector<char>(26, 0));
  vector<char> mark(26, false);
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    for (char c : s) {
      mark[c - 'a'] = true;
    }
    for (int j = 1; j < (int)s.size(); j++) {
      mat[s[j - 1] - 'a'][s[j] - 'a'] = 1;
    }
  }
  vector<int> kntIn(26, 0), kntOut(26, 0);
  for (int i = 0; i < 26; i++) {
    if (mat[i][i]) {
      return false;
    }
    for (int j = 0; j < 26; j++) {
      kntIn[i] += mat[j][i];
      kntOut[i] += mat[i][j];
    }
    if (kntIn[i] > 1 || kntOut[i] > 1) {
      return false;
    }
  }
  vector<string> results;
  int checked = 0;
  for (int i = 0; i < 26; i++) {
    if (!mark[i]) {
      checked++;
      continue;
    }
    if (kntIn[i] != 0) {
      continue;
    }
    int qur = i;
    results.emplace_back();
    string &s = results.back();
    s += char(qur + 'a');
    checked++;
    while (kntOut[qur] != 0) {
      for (int j = 0; j < 26; j++) {
        if (mat[qur][j]) {
          qur = j;
          break;
        }
      }
      s += char(qur + 'a');
      checked++;
    }
  }
  if (checked != 26) {
    return false;
  }
  sort(results.begin(), results.end());
  for (string s : results) {
    cout << s;
  }
  cout << endl;
  return true;
}
int main() {
  if (!mainHook()) {
    cout << "NO" << endl;
  }
  return 0;
}
