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 S[100005];
bool nex[26][26], used[26];
void die() {
  printf("NO\n");
  exit(0);
}
void go(int x) {
  if (used[x]) die();
  used[x] = true;
  for (int y = 0; y < 26; ++y)
    if (nex[x][y]) {
      go(y);
    }
}
int indeg[26], outdeg[26];
bool inside[26];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    scanf("%s", S);
    int len = strlen(S);
    for (int j = 0; j < len; ++j) inside[S[j] - 'a'] = true;
    for (int j = 0; j < len - 1; ++j) {
      if (nex[S[j] - 'a'][S[j + 1] - 'a']) continue;
      nex[S[j] - 'a'][S[j + 1] - 'a'] = true;
      ++indeg[S[j + 1] - 'a'];
      ++outdeg[S[j] - 'a'];
    }
  }
  for (int i = 0; i < 26; ++i)
    if (indeg[i] > 1 || outdeg[i] > 1) die();
  for (int i = 0; i < 26; ++i) {
    memset(used, 0, sizeof(used));
    go(i);
  }
  vector<string> strs;
  for (int i = 0; i < 26; ++i)
    if (!indeg[i] && inside[i]) {
      int v = i;
      string s;
      for (;;) {
        s += 'a' + v;
        int vv = v;
        for (int j = 0; j < 26; ++j)
          if (nex[v][j]) {
            v = j;
            break;
          }
        if (v == vv) break;
      }
      strs.push_back(s);
    }
  sort(strs.begin(), strs.end());
  for (auto s : strs) printf("%s", s.c_str());
  printf("\n");
}
