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;
set<char> nextc[200], prevc[200];
int reqd[200], visited[200];
void process(string &s) {
  if (s.length() < 2) {
    reqd[s[0]] = 1;
    return;
  }
  for_each(s.begin(), s.end(), [](char x) { reqd[(x)] = 1; });
  nextc[s[0]].insert(s[1]);
  for (int i = 1; i < s.length() - 1; i++) {
    nextc[s[i]].insert(s[i + 1]);
    prevc[s[i]].insert(s[i - 1]);
  }
  prevc[s.back()].insert(s[s.length() - 2]);
}
int main(int argc, const char **argv) {
  if (argc >= 2) {
    freopen(argv[1], "r", stdin);
  }
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    process(s);
  }
  vector<string> candidates;
  for (int i = 'a'; i <= 'z'; i++) {
    cerr << (char)i << " " << reqd[i] << endl;
    if (prevc[i].size() > 1 || nextc[i].size() > 1) {
      cout << "NO" << endl;
      return 0;
    }
  }
  for (int i = 'a'; i <= 'z'; i++) {
    if (prevc[i].empty() && reqd[i]) {
      string s = "";
      auto c = i;
      s += c;
      reqd[c] = 0;
      while (nextc[c].empty() == false) {
        c = *nextc[c].begin();
        s += c;
        reqd[c] = 0;
      }
      candidates.push_back(s);
    }
  }
  for (int i = 0; i < 200; i++) {
    if (reqd[i]) {
      cout << "NO" << endl;
      return 0;
    }
  }
  sort(candidates.begin(), candidates.end());
  for (auto candidate : candidates) {
    cout << candidate;
  }
  cout << endl;
}
