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;
int i, j, m, n, len[100005], head[100005], cnt[30], tot, t, temp;
string s[100005];
bool used[30], happen[30], found, finish[100005];
int ans[30], nxt;
int main() {
  tot = 0;
  memset(cnt, 0, sizeof(cnt));
  memset(happen, false, sizeof(happen));
  memset(head, 0, sizeof(head));
  memset(finish, false, sizeof(finish));
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    cin >> s[i];
    len[i] = s[i].length();
    memset(used, false, sizeof(used));
    for (j = 0; j <= len[i] - 1; j++) {
      if (used[s[i][j] - 'a']) {
        printf("NO\n");
        return 0;
      }
      used[s[i][j] - 'a'] = true;
      happen[s[i][j] - 'a'] = true;
      if (j > 0) cnt[s[i][j] - 'a']++;
    }
  }
  for (i = 0; i <= 25; i++) {
    if (happen[i]) tot++;
  }
  nxt = -1;
  for (i = 1; i <= tot; i++) {
    found = false;
    if (nxt != -1) {
      if (cnt[nxt] != 0) {
        printf("NO\n");
        return 0;
      }
      j = nxt;
      nxt = -1;
      for (t = 1; t <= n; t++) {
        if (!finish[t]) {
          if (s[t][head[t]] - 'a' == j) {
            head[t]++;
            if (head[t] < len[t]) {
              cnt[s[t][head[t]] - 'a']--;
              if (nxt == -1) {
                nxt = s[t][head[t]] - 'a';
              } else {
                if (nxt != s[t][head[t]] - 'a') {
                  printf("NO\n");
                  return 0;
                }
              }
            } else {
              finish[t] = true;
            }
          }
        }
      }
      happen[j] = false;
      ans[i] = j + 'a';
    } else {
      for (j = 0; j <= 25; j++) {
        if (happen[j]) {
          if (cnt[j] == 0) {
            nxt = -1;
            for (t = 1; t <= n; t++) {
              if (!finish[t]) {
                if (s[t][head[t]] - 'a' == j) {
                  head[t]++;
                  if (head[t] < len[t]) {
                    cnt[s[t][head[t]] - 'a']--;
                    if (nxt == -1) {
                      nxt = s[t][head[t]] - 'a';
                    } else {
                      if (nxt != s[t][head[t]] - 'a') {
                        printf("NO\n");
                        return 0;
                      }
                    }
                  } else
                    finish[t] = true;
                }
              }
            }
            ans[i] = j + 'a';
            happen[j] = false;
            found = true;
          }
        }
        if (found) break;
      }
      if (!found) {
        printf("NO\n");
        return 0;
      }
    }
  }
  for (i = 1; i <= tot; i++) {
    printf("%c", ans[i]);
  }
  printf("\n");
  return 0;
}
