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>
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
using namespace std;
const int N = 200003, mod = 1e9 + 7;
const long long inf = (1e18 + 11);
int freq[26], indeg[26], pres[26];
unordered_set<int> g[26];
string ans;
void dfs(int i) {
  bool f = 0;
  ans += (char)(i + 'a');
  for (auto it : g[i]) {
    if (f) ans += (char)(i + 'a');
    --indeg[it];
    if (!indeg[it]) --indeg[it];
    dfs(it);
    f = 1;
  }
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  int i, j, x, y, sz;
  char ch;
  string s;
  for (j = 0; j < n; ++j) {
    cin >> s;
    sz = s.size();
    fill(freq, freq + 26, 0);
    freq[s[0] - 'a']++;
    pres[s[0] - 'a']++;
    for (i = 1; i < sz; ++i) {
      if (g[s[i] - 'a'].count(s[i - 1] - 'a')) return cout << "NO", 0;
      g[s[i - 1] - 'a'].insert(s[i] - 'a');
      ++freq[s[i] - 'a'];
      ++indeg[s[i] - 'a'];
      pres[s[i] - 'a']++;
    }
    for (i = 0; i < 26; ++i)
      if (freq[i] > 1) return cout << "NO", 0;
  }
  ans = "";
  for (i = 0; i < 26; ++i)
    if (pres[i] and !indeg[i]) dfs(i);
  fill(freq, freq + 26, 0);
  sz = ans.size();
  for (i = 0; i < sz; ++i) freq[ans[i] - 'a']++;
  x = 0;
  for (i = 0; i < 26; ++i) {
    if (pres[i] and !freq[i]) return cout << "NO", 0;
    if (!freq[i] or freq[i] == x)
      continue;
    else if (!x)
      x = freq[i];
    else
      return cout << "NO", 0;
  }
  if (!ans.size()) ans = "NO";
  cout << ans;
  return 0;
}
