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 N = 300;
bool b[N], d[N];
int c[N];
int main() {
  ios_base::sync_with_stdio(false);
  int i, j, n;
  set<char> se[N];
  set<int> p;
  vector<char> e[N];
  cin >> n;
  string s1, s;
  s1 = "";
  for (i = 0; i < n; ++i) {
    cin >> s;
    p.clear();
    for (j = 0; j < s.size(); ++j) {
      if (p.find(s[j]) != p.end()) {
        cout << "NO";
        return 0;
      } else
        p.insert(s[j]);
      d[s[j]] = true;
    }
    for (j = 0; j < s.size() - 1; ++j) {
      if (se[s[j]].find(s[j + 1]) == se[s[j]].end())
        e[s[j]].push_back(s[j + 1]);
      se[s[j]].insert(s[j + 1]);
    }
  }
  for (i = 0; i < 256; ++i)
    if (e[i].size() > 1) {
      cout << "NO";
      return 0;
    } else {
      for (j = 0; j < e[i].size(); ++j) c[e[i][j]]++;
    }
  int tf = 0;
  s1 = "";
  for (i = 0; i < 256; ++i) {
    if (c[i] > 1) {
      cout << "NO";
      return 0;
    }
  }
  for (i = 0; i < 256; ++i)
    if ((c[i] == 0) && (!b[i]) && (d[i])) {
      b[i] = true;
      s1 += (char)i;
      j = i;
      while (e[j].size() == 1) {
        j = e[j][0];
        s1 += char(j);
        b[j] = true;
      }
    }
  for (i = 0; i < 256; ++i)
    if ((d[i]) && (!b[i])) {
      cout << "NO";
      return 0;
    }
  cout << s1;
}
