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;
struct Str {
  string s;
  int cnt[26], first[26];
  Str() : s("") {
    for (int i = 0; i < 26; i++) cnt[i] = 0, first[i] = -1;
  }
  Str(string _s) : s(_s) {
    for (int i = 0; i < 26; i++) cnt[i] = 0, first[i] = -1;
    int i = 0;
    for (char c : _s) {
      cnt[c - 'a']++;
      if (first[c - 'a'] == -1) first[c - 'a'] = i;
      i++;
    }
  }
};
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  set<Str*> st;
  bool fail = false;
  for (int i = 0; i < n; i++) {
    string str;
    cin >> str;
    st.insert(new Str(str));
  }
  for (int i = 0; i < 26; i++) {
    vector<Str*> tmp;
    for (auto it = st.begin(); it != st.end();) {
      if ((*it)->cnt[i]) {
        tmp.push_back(*it);
        st.erase(it++);
      } else {
        it++;
      }
    }
    deque<char> strFact;
    string newStr;
    if (tmp.empty()) continue;
    for (int d = 0;; d++) {
      char c = '\0';
      for (auto t : tmp) {
        if (t->first[i] + d >= (int)t->s.size()) continue;
        if (!c) c = t->s[t->first[i] + d];
        if (t->s[t->first[i] + d] != c) {
          fail = true;
          goto End;
        }
      }
      if (c)
        strFact.push_back(c);
      else
        break;
    }
    for (int d = 1;; d++) {
      char c = '\0';
      for (auto t : tmp) {
        if (t->first[i] - d < 0) continue;
        if (!c) c = t->s[t->first[i] - d];
        if (t->s[t->first[i] - d] != c) {
          fail = true;
          goto End;
        }
      }
      if (c)
        strFact.push_front(c);
      else
        break;
    }
    for (Str* t : tmp) delete t;
    for (char c : strFact) newStr.push_back(c);
    st.insert(new Str(newStr));
  }
End:
  if (!fail) {
    vector<string> vect;
    map<char, int> mp;
    for (auto s : st) {
      vect.push_back(s->s);
      for (char c : s->s) mp[c]++;
    }
    for (auto& p : mp) {
      if (p.second > 1) {
        cout << "NO";
        return 0;
      }
    }
    sort(vect.begin(), vect.end());
    for (auto s : vect) cout << s;
  } else {
    cout << "NO";
  }
}
