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 inf = INT_MAX;
const long long llinf = LONG_LONG_MAX;
string ans;
int cnt[30];
int us[30];
vector<set<int>> g(30);
int deg[30];
void dfs(int u) {
  ans += (char)(u + 'a');
  us[u] = 1;
  for (auto to : g[u]) {
    if (us[to]) {
      cout << "NO";
      exit(0);
    }
    dfs(to);
  }
}
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    for (auto x : s) {
      cnt[x - 'a']++;
    }
    for (int i = 0; i < (int)s.size() - 1; i++) {
      int u = s[i] - 'a';
      int v = s[i + 1] - 'a';
      if (g[u].count(v) == 0) {
        if (g[v].count(u)) {
          cout << "NO";
          return 0;
        }
        g[u].insert(v);
        if (g[u].size() > 1) {
          cout << "NO";
          return 0;
        }
        deg[v]++;
      }
    }
  }
  vector<string> ss;
  for (int i = 0; i < 26; i++) {
    if (!us[i] && cnt[i] && !deg[i]) {
      ans.clear();
      dfs(i);
      ss.push_back(ans);
    }
  }
  sort(ss.begin(), ss.end());
  if (ss.empty()) {
    cout << "NO";
    return 0;
  }
  int p[30];
  memset(p, 0, sizeof p);
  for (auto x : ss) {
    for (auto y : x) p[y - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    if (cnt[i] && !p[i]) {
      cout << "NO";
      return 0;
    }
  }
  for (auto x : ss) cout << x;
  return 0;
}
