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>
const int MAX_N = 1e5 + 5;
int n, m;
char str[MAX_N], nxt[256];
bool chk[256], vis[256], not_root[256], flag;
std::vector<char> ans;
void dfs(char c) {
  if (!vis[c]) {
    vis[c] = true;
    ans.push_back(c);
    if (nxt[c]) dfs(nxt[c]);
  } else
    flag = true;
}
int main() {
  scanf("%d", &n);
  while (n--) {
    scanf(" %s", str);
    m = strlen(str);
    for (int i = 0; i < m; ++i) chk[str[i]] = true;
    for (int i = 0; i + 1 < m; ++i) {
      if (nxt[str[i]] == 0)
        nxt[str[i]] = str[i + 1];
      else if (nxt[str[i]] != str[i + 1]) {
        printf("NO\n");
        return 0;
      }
      not_root[str[i + 1]] = true;
    }
  }
  for (char i = 'a'; i <= 'z'; ++i)
    if (!not_root[i] && chk[i]) dfs(i);
  for (char i = 'a'; i <= 'z'; ++i) flag |= chk[i] != vis[i];
  if (flag) {
    printf("NO\n");
    return 0;
  }
  for (char c : ans) printf("%c", c);
  printf("\n");
  return 0;
}
