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;
long long n;
vector<string> s;
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  s.resize(n);
  for (long long i = 0; i < n; i++) {
    cin >> s[i];
  }
  bool fail = false;
  long long cnt[200];
  for (auto x : s) {
    if (x.length() > 'z' - 'a' + 1) {
      fail = true;
      break;
    }
    for (char c = 0; c < 127; c++) cnt[c] = 0;
    for (auto c : x) {
      if (++cnt[c] > 1) {
        fail = true;
        break;
      }
    }
    if (fail) break;
  }
  if (fail) {
    cout << "NO\n";
    return 0;
  }
  for (auto x : s)
    for (auto c : x) cnt[c] = 1;
  char ne[200];
  char pr[200];
  for (char c = 0; c < 127; c++) pr[c] = ne[c] = 0;
  for (auto x : s) {
    for (long long i = 0; i + 1 < x.length(); i++) {
      if (ne[x[i]] != 0 && ne[x[i]] != x[i + 1]) {
        fail = true;
        break;
      }
      if (pr[x[i + 1]] != 0 && pr[x[i + 1]] != x[i]) {
        fail = true;
        break;
      }
      ne[x[i]] = x[i + 1];
      pr[x[i + 1]] = x[i];
    }
    if (fail) break;
  }
  if (fail) {
    cout << "NO\n";
    return 0;
  }
  string res = "";
  for (char c = 'a'; c <= 'z'; c++) {
    char z = c;
    if (pr[c]) continue;
    while (cnt[z]) {
      res.push_back(z);
      cnt[z] = 0;
      z = ne[z];
    }
  }
  for (char c = 'a'; c <= 'z'; c++) {
    if (cnt[c]) fail = true;
  }
  if (fail) {
    cout << "NO\n";
    return 0;
  }
  cout << res << "\n";
  return 0;
}
