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;
bool isvalid(string s) {
  sort(s.begin(), s.end());
  for (int i = 1; i < s.size(); ++i) {
    if (s[i] == s[i - 1]) return false;
  }
  return true;
}
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<string> s(n);
  for (int i = 0; i < n; ++i) {
    cin >> s[i];
  }
  if (n > 26 * 27 / 2) {
    cout << "NO\n";
  } else {
    vector<string> ret;
    string cur = s[0];
    s.erase(s.begin());
    while (!s.empty()) {
      bool found = false;
      for (int i = 0; i < s.size() && !found; ++i) {
        if (cur.find(s[i]) != string::npos) {
          s.erase(s.begin() + i);
          found = true;
          break;
        }
        if (s[i].find(cur) != string::npos) {
          cur = s[i];
          s.erase(s.begin() + i);
          found = true;
        }
        for (int j = 1; j < s[i].size() && j < cur.size(); ++j) {
          if (cur.substr(0, j) == s[i].substr(s[i].size() - j)) {
            string cand = s[i].substr(0, s[i].size() - j) + cur;
            if (isvalid(cand)) {
              cur = cand;
              s.erase(s.begin() + i);
              found = true;
            }
            break;
          }
          if (cur.substr(cur.size() - j) == s[i].substr(0, j)) {
            string cand = cur + s[i].substr(j);
            if (isvalid(cand)) {
              cur = cand;
              s.erase(s.begin() + i);
              found = true;
            }
            break;
          }
        }
      }
      if (!found) {
        ret.push_back(cur);
        cur = s[0];
        s.erase(s.begin());
      }
    }
    ret.push_back(cur);
    sort(ret.begin(), ret.end());
    string conc;
    for (string i : ret) {
      conc += i;
    }
    cout << (isvalid(conc) ? conc : "NO") << "\n";
  }
  return 0;
}
