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 ok[256];
bool used[256];
char nx[256];
char pr[256];
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    char ls = 0;
    for (auto c : s) {
      ok[c] = true;
      if (ls != 0) {
        if ((nx[ls] != 0 && nx[ls] != c) || (pr[c] != 0 && pr[c] != ls)) {
          cout << "NO";
          return 0;
        }
        nx[ls] = c;
        pr[c] = ls;
      }
      ls = c;
    }
  }
  string ans = "";
  for (char c = 'a'; c <= 'z'; c++) {
    if (ok[c] && pr[c] == 0) {
      char d = c;
      while (d != 0 && !used[d]) {
        used[d] = true;
        ans.push_back(d);
        d = nx[d];
      }
      if (used[d]) {
        cout << "NO";
        return 0;
      }
    }
  }
  for (char c = 'a'; c <= 'z'; c++) {
    if (ok[c] && !used[c]) {
      cout << "NO";
      return 0;
    }
  }
  cout << ans;
  return 0;
}
