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>
const long long INF = 1e18L + 1;
const int IINF = 1e9 + 1;
using namespace std;
template <class TH>
void _dbg(const char *sdbg, TH h) {
  cerr << sdbg << '=' << h << endl;
}
template <class TH, class... TA>
void _dbg(const char *sdbg, TH h, TA... a) {
  while (*sdbg != ',') cerr << *sdbg++;
  cerr << '=' << h << ',';
  _dbg(sdbg + 1, a...);
}
int n;
vector<string> s;
vector<set<int>> v(26);
int deg[26], odw[26];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  s.resize(n);
  set<char> lit;
  for (long long i = (long long)0; i < (long long)n; i++) {
    cin >> s[i];
    for (auto x : s[i]) {
      lit.insert(x);
    }
    for (long long j = (long long)1; j < (long long)(int)((s[i]).size()); j++) {
      v[s[i][j - 1] - 'a'].insert(s[i][j] - 'a');
    }
  }
  for (long long i = (long long)0; i < (long long)26; i++) {
    if ((int)((v[i]).size()) > 0) {
      deg[*v[i].begin()]++;
    }
  }
  for (long long i = (long long)0; i < (long long)26; i++) {
    (i, (char)('a' + i), (int)((v[i]).size()), deg[i]);
    if ((int)((v[i]).size()) > 1 or deg[i] > 1) {
      cout << "NO";
      return 0;
    }
  }
  vector<int> wyn;
  for (long long i = (long long)0; i < (long long)26; i++) {
    if (!odw[i] and deg[i] == 0 and lit.find('a' + i) != lit.end()) {
      int x = i;
      wyn.push_back(x);
      odw[x] = 1;
      while ((int)((v[x]).size()) == 1) {
        x = *v[x].begin();
        wyn.push_back(x);
        odw[x] = 1;
      }
    }
  }
  if ((int)((wyn).size()) != (int)((lit).size())) {
    cout << "NO";
    return 0;
  }
  for (auto x : wyn) {
    cout << (char)('a' + x);
  }
  return 0;
}
