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;
template <class T>
void splitstr(const string &s, vector<T> &out) {
  istringstream in(s);
  out.clear();
  copy(istream_iterator<T>(in), istream_iterator<T>(), back_inserter(out));
}
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
static void redirect(int argc, const char **argv) {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  if (argc > 1) {
    static filebuf f;
    f.open(argv[1], ios::in);
    cin.rdbuf(&f);
    if (!cin) {
      cerr << "Failed to open '" << argv[1] << "'" << endl;
      exit(1);
    }
  }
  if (argc > 2) {
    static filebuf f;
    f.open(argv[2], ios::out | ios::trunc);
    cout.rdbuf(&f);
    if (!cout) {
      cerr << "Failed to open '" << argv[2] << "'" << endl;
    }
  }
}
int main(int argc, const char **argv) {
  redirect(argc, argv);
  int N;
  cin >> N;
  array<int, 26> follow;
  for (int i = 0; i < 26; i++) follow[i] = -1;
  int use = 0;
  for (int i = 0; i < N; i++) {
    string word;
    cin >> word;
    for (char c : word) use |= 1 << (c - 'a');
    for (int j = 0; j < ((long long)(word).size()) - 1; j++) {
      int a = word[j] - 'a';
      int b = word[j + 1] - 'a';
      if (follow[a] != -1 && follow[a] != b) {
        cout << "NO\n";
        return 0;
      }
      follow[a] = b;
    }
  }
  array<int, 26> deg{};
  for (int i = 0; i < 26; i++)
    if (follow[i] != -1) deg[follow[i]]++;
  for (int i = 0; i < 26; i++)
    if (deg[i] > 1) {
      cout << "NO\n";
      return 0;
    }
  vector<string> chains;
  for (int i = 0; i < 26; i++) {
    if ((use & (1 << i)) && !deg[i]) {
      string chain;
      for (int j = i; j != -1; j = follow[j]) chain += 'a' + j;
      chains.push_back(chain);
    }
  }
  sort(begin(chains), end(chains));
  string out;
  for (const string &c : chains) out += c;
  if (((long long)(out).size()) != __builtin_popcount(use))
    cout << "NO\n";
  else
    cout << out << "\n";
  return 0;
}
