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 g[26][26];
bool vis[26];
int in[26], out[26];
int sig[26];
vector<char> ans;
bool dfs(int i) {
  vis[i] = true;
  ans.push_back(char(i + 'a'));
  for (int j = 0; j < 26; j++) {
    if (g[i][j]) {
      if (!vis[j])
        return dfs(j);
      else
        return false;
    }
  }
  return true;
}
int main() {
  int n;
  cin >> n;
  string s;
  for (int i = 0; i < n; i++) {
    cin >> s;
    for (int j = 0; j < s.size() - 1; j++) {
      g[s[j] - 'a'][s[j + 1] - 'a'] = 1;
    }
    if (s.size() == 1) {
      sig[s[0] - 'a'] = 1;
    }
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < 26; j++) {
      if (g[i][j]) {
        out[i]++;
        in[j]++;
      }
    }
  }
  bool can = true;
  for (int i = 0; i < 26; i++) {
    if (in[i] > 1 || out[i] > 1 || g[i][i]) {
      can = false;
    }
  }
  memset(vis, 0, sizeof(vis));
  for (int i = 0; i < 26; i++) {
    if (out[i] && !in[i]) {
      if (!dfs(i)) {
        can = false;
        break;
      }
    }
    if (sig[i] && in[i] == 0 && out[i] == 0) {
      ans.push_back(char(i + 'a'));
    }
  }
  for (int i = 0; i < 26; i++) {
    if (out[i] || in[i]) {
      if (!vis[i]) can = false;
    }
  }
  if (!can) {
    cout << "NO" << endl;
  } else {
    for (int i = 0; i < ans.size(); i++) {
      cout << ans[i];
    }
    cout << endl;
  }
  return 0;
}
