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 INF = 1000000007;
const double eps = 0.000001;
bool check(string s1, string s, unordered_set<string> &st) {
  char c = s[0];
  int i = 0;
  for (; i < s1.size(); i++)
    if (s1[i] == c) break;
  if (i == s1.size()) return false;
  st.erase(s1);
  st.erase(s);
  int j = 0;
  while (j < s.size() && i < s1.size()) {
    if (s1[i] != s[j]) {
      cout << "NO";
      exit(0);
    }
    j++;
    i++;
  }
  for (; j < s.size(); j++) s1.push_back(s[j]);
  st.insert(s1);
  return true;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  unordered_set<string> st;
  string s;
  for (int i = 0; i < n; i++) {
    cin >> s;
    unordered_map<char, int> m;
    for (char c : s) {
      m[c]++;
      if (m[c] > 1) {
        cout << "NO";
        return 0;
      }
    }
    st.insert(s);
  }
  if (st.size() > 351) {
    cout << "NO";
    return 0;
  }
  vector<string> v;
  while (st.size()) {
    s = *st.begin();
    bool flag = true;
    for (string s1 : st) {
      if (s1 == s) continue;
      if (check(s1, s, st)) {
        flag = false;
        break;
      }
      if (check(s, s1, st)) {
        flag = false;
        break;
      }
    }
    if (flag) {
      v.push_back(s);
      st.erase(s);
    }
  }
  sort(v.begin(), v.end());
  unordered_map<char, int> m;
  for (string s1 : v)
    for (char c1 : s1) {
      m[c1]++;
      if (m[c1] > 1) {
        cout << "NO";
        return 0;
      }
    }
  for (string s1 : v) cout << s1;
  return 0;
}
