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 a[26][2];
string s;
bool s_merge(string fir, string sec) {
  int pos1, pos2;
  for (int i = 0; i < 26; i++)
    if (a[i][0] != -1 && a[i][1] != -1) {
      pos1 = a[i][0];
      pos2 = a[i][1];
      break;
    }
  if (pos1 < pos2) {
    swap(pos1, pos2);
    swap(fir, sec);
  }
  s = fir;
  int pos;
  for (int i = 0; i < sec.length(); i++) {
    pos = i + pos1 - pos2;
    if (pos < fir.length()) {
      if (s[pos] != sec[i]) return false;
    } else
      s += sec[i];
  }
  return true;
}
bool same_sim() {
  for (int i = 0; i < 26; i++)
    if (a[i][0] != -1 && a[i][1] != -1) return true;
  return false;
}
void make_arr(string s, int arr) {
  for (int i = 0; i < 26; i++) a[i][arr] = -1;
  int num;
  for (int i = 0; i < s.length(); i++) {
    num = (int)(s[i] - 'a');
    a[num][arr] = i;
  }
}
bool check(string s) {
  bool sim[26] = {};
  int num;
  for (int i = 0; i < s.length(); i++) {
    num = (int)(s[i] - 'a');
    if (sim[num])
      return false;
    else
      sim[num] = true;
  }
  return true;
}
vector<string> st;
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s;
    if (check(s)) {
      bool fl = true;
      while (fl) {
        fl = false;
        make_arr(s, 1);
        for (int to = 0; to < st.size(); to++) {
          make_arr(st[to], 0);
          if (!same_sim()) continue;
          if (s_merge(st[to], s)) {
            st.erase(st.begin() + to);
            if (!check(s)) {
              cout << "NO";
              return 0;
            }
            fl = true;
            break;
          } else {
            cout << "NO";
            return 0;
          }
        }
      }
      st.push_back(s);
    } else {
      cout << "NO";
      return 0;
    }
  }
  sort(st.begin(), st.end());
  for (int i = 0; i < st.size(); i++) cout << st[i];
  return 0;
}
