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;
using ll = long long;
using vi = vector<int>;
using db = double;
int n;
char s_[100006];
string s[100006];
int nx[128];
int deg[128];
bool v[128];
string t;
int main() {
  cin >> n;
  fill(v, end(v), true);
  for (int i = 1; i <= n; ++i) {
    scanf("%s", s_);
    s[i] = s_;
    for (int j = 0; j + 1 < s[i].size(); ++j) nx[s[i][j]] = s[i][j + 1];
    for (auto j : s[i]) v[j] = false;
  }
  for (int i = 'a'; i <= 'z'; ++i) ++deg[nx[i]];
  for (int i = 'a'; i <= 'z'; ++i)
    if (!v[i] && !deg[i]) {
      for (int j = i; j && !v[j]; j = nx[j]) {
        t.push_back(j);
        v[j] = true;
      }
    }
  fill(nx, end(nx), 0);
  for (int i = 0; i + 1 < t.size(); ++i) nx[t[i]] = t[i + 1];
  fill(v, end(v), false);
  for (auto i : t) v[i] = true;
  for (int i = 1; i <= n; ++i) {
    for (int j = 0; j + 1 < s[i].size(); ++j)
      ({
        if (!(nx[s[i][j]] == s[i][j + 1]))
          ({
            puts("NO");
            exit(0);
          });
      });
    for (auto j : s[i])
      ({
        if (!(v[j]))
          ({
            puts("NO");
            exit(0);
          });
      });
  }
  cout << t << endl;
  return 0;
}
