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;
char second[100005];
string arr[100005];
int cnt[27];
bool nxt[30][30];
int in[30], out[30];
int mask;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    scanf("%s", second);
    arr[i] = string(second);
    memset(cnt, 0, sizeof(cnt));
    for (int j = 0; j < arr[i].size(); j++) {
      cnt[arr[i][j] - 'a']++;
      mask |= (1 << (arr[i][j] - 'a'));
    }
    for (int j = 0; j < 26; j++) {
      if (cnt[j] > 1) {
        cout << "NO";
        return 0;
      }
    }
    for (int j = 0; j + 1 < arr[i].size(); j++) {
      if (!nxt[arr[i][j] - 'a'][arr[i][j + 1] - 'a']) {
        nxt[arr[i][j] - 'a'][arr[i][j + 1] - 'a'] = true;
        in[arr[i][j + 1] - 'a']++;
        out[arr[i][j] - 'a']++;
      }
    }
  }
  for (int i = 0; i < 26; i++) {
    if (in[i] > 1 || out[i] > 1) {
      cout << "NO";
      return 0;
    }
  }
  string ans = "";
  for (int i = 0; i < 26; i++) {
    if (mask & (1 << i)) {
      if (in[i] == 0) {
        int x = i;
        while (1) {
          int next = -1;
          ans += (char)(x + 'a');
          mask ^= (1 << x);
          for (int j = 0; j < 26; j++) {
            if (mask & (1 << j)) {
              if (nxt[x][j]) next = j;
            }
          }
          if (next == -1) break;
          x = next;
        }
      }
    }
  }
  if (mask != 0)
    cout << "NO";
  else
    cout << ans;
  return 0;
}
