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;
const int A = 26;
set<int> adj[A];
bool need[A];
int color[A];
int cnt[A];
void dfs(int u) {
  if (adj[u].size() > 1u) {
    cout << "NO\n";
    exit(0);
  }
  color[u] = 1;
  for (auto c : adj[u]) {
    ++cnt[c];
    if (color[c] == 1) {
      cout << "NO\n";
      exit(0);
    } else if (color[c] == 0) {
      dfs(c);
    }
  }
  color[u] = 2;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    string s;
    cin >> s;
    for (auto &j : s) {
      j -= 'a';
      need[j] = true;
    }
    for (int j = 1; j < int(s.size()); ++j) {
      adj[s[j - 1]].insert(s[j]);
    }
  }
  for (int i = 0; i < A; ++i) {
    if (need[i] && color[i] == 0) {
      dfs(i);
    }
  }
  if (*max_element(cnt, cnt + A) > 1) {
    cout << "NO\n";
    exit(0);
  }
  for (int i = 0; i < A; ++i) {
    if (need[i] && cnt[i] == 0) {
      int j = i;
      while (!adj[j].empty()) {
        cout << char(j + 'a');
        j = *adj[j].begin();
      }
      cout << char(j + 'a');
    }
  }
  cout << "\n";
}
