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 fa[100005];
int gfa(int a) {
  if (fa[a] == a) return a;
  return fa[a] = gfa(fa[a]);
}
int nx[100005], pre[100005];
bool flag = 1;
void lk(int a, int b) {
  if (nx[a] == b) return;
  if (gfa(a) == gfa(b)) flag = 0;
  if (nx[a]) flag = 0;
  if (pre[b]) flag = 0;
  nx[a] = b, pre[b] = a;
  fa[gfa(a)] = gfa(b);
}
char inp[100005];
bool hv[100005];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= 26; i++) fa[i] = i;
  for (int i = 1; i <= n; i++) {
    scanf("%s", inp);
    int l = strlen(inp);
    for (int j = 0; j < l; j++) hv[inp[j] - 'a' + 1] = 1;
    for (int j = 0; j < l - 1; j++) lk(inp[j] - 'a' + 1, inp[j + 1] - 'a' + 1);
  }
  if (!flag)
    printf("NO\n");
  else {
    for (int i = 1; i <= 26; i++)
      if (pre[i] || !hv[i])
        continue;
      else {
        int npl = i;
        while (npl) printf("%c", char('a' + npl - 1)), npl = nx[npl];
      }
    printf("\n");
  }
  return 0;
}
