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 NMax = 100003;
const int SIGMA = 130;
int n, nr;
int viz[SIGMA], edge[SIGMA], st[SIGMA], used[SIGMA], EDG[NMax], rev[NMax];
string x;
string tab[NMax];
void dfs(int nod) {
  viz[nod] = 1;
  if (!viz[edge[nod]] && edge[nod]) dfs(edge[nod]);
  st[++nr] = nod;
}
bool cmp(string x, string y) { return (x > y); }
int main() {
  cin >> n;
  cin.get();
  for (int i = 0; i < n; ++i) {
    cin >> x;
    for (int j = 0; j < x.size() - 1; ++j) {
      used[x[j]] = 1;
      if (edge[x[j]] && edge[x[j]] != x[j + 1]) {
        cout << "NO" << '\n';
        return 0;
      }
      rev[x[j + 1]] = x[j];
      edge[x[j]] = x[j + 1];
    }
    used[x[x.size() - 1]] = 1;
    tab[i + 1] = x;
  }
  sort(tab + 1, tab + 1 + n, cmp);
  for (int i = 1; i <= n; ++i) {
    if (!viz[tab[i][0]] && rev[tab[i][0]] == 0) {
      dfs(tab[i][0]);
    }
  }
  for (int i = 1; i <= n; ++i) {
    if (!viz[tab[i][0]]) {
      dfs(tab[i][0]);
    }
  }
  string ans;
  for (int i = nr; i >= 1; --i) {
    ans += st[i];
  }
  for (int i = 1; i <= n; ++i) {
    if (ans.find(tab[i]) == string::npos) {
      cout << "NO";
      return 0;
    }
  }
  cout << ans << '\n';
  return 0;
}
