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 n;
char s[101101];
bool chk;
bool occ[33];
int ideg[33], odeg[33];
char ans[33], la;
void add_edge(char ch1, char ch2) {
  ch1 -= 'a';
  ch2 -= 'a';
  if (odeg[ch1] == -1)
    odeg[ch1] = ch2;
  else if (odeg[ch1] != ch2)
    chk = false;
  if (ideg[ch2] == -1)
    ideg[ch2] = ch1;
  else if (ideg[ch2] != ch1)
    chk = false;
}
void dfs(int cur) {
  occ[cur] = false;
  ans[la++] = cur + 'a';
  if (odeg[cur] != -1) dfs(odeg[cur]);
}
int main() {
  scanf("%d", &n);
  chk = true;
  memset(occ, false, sizeof occ);
  memset(ideg, -1, sizeof ideg);
  memset(odeg, -1, sizeof odeg);
  for (int i = 0; i < n; i++) {
    scanf("%s", s);
    int len = strlen(s);
    for (int j = 0; j < len; j++) occ[s[j] - 'a'] = true;
    for (int j = 1; j < len; j++) add_edge(s[j - 1], s[j]);
    sort(s, s + len);
    for (int j = 1; j < len; j++)
      if (s[j] == s[j - 1]) chk = false;
  }
  if (chk) {
    la = 0;
    for (int i = 0; i < 26; i++)
      if (occ[i] && ideg[i] < 0) dfs(i);
    for (int i = 0; i < 26; i++)
      if (occ[i]) chk = false;
  }
  if (chk) {
    for (int i = 0; i < la; i++) putchar(ans[i]);
    puts("");
  } else {
    puts("NO");
  }
  return 0;
}
