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;
vector<vector<int>> adj;
bool che;
int co[26];
void dfs(int v) {
  co[v] = 1;
  for (auto u : adj[v]) {
    if (co[u] == 1) {
      che = 1;
    }
    if (co[u] == 0) {
      dfs(u);
    }
  }
  co[v] = 2;
}
int main() {
  int n;
  cin >> n;
  adj.resize(26);
  bool b = 1;
  int pa[26];
  for (int i = 0; i < 26; i++) {
    pa[i] = -1;
  }
  bool ex[26];
  for (int i = 0; i < 26; i++) {
    ex[i] = 0;
  }
  for (int i = 0; i < n; i++) {
    string second;
    cin >> second;
    ex[(second[0] - 'a')] = 1;
    string t;
    t = second;
    sort(t.begin(), t.end());
    for (int j = 0; j < t.size() - 1; j++) {
      if (t[j] == t[j + 1]) {
        cout << "NO";
        return 0;
      }
    }
    for (int i = 0; i < second.size() - 1; i++) {
      if (pa[(second[i] - 'a')] != -1 &&
          pa[(second[i] - 'a')] != (second[(i + 1)] - 'a')) {
        cout << "NO";
        return 0;
      }
      pa[(second[i] - 'a')] = (second[(i + 1)] - 'a');
      ex[(second[i] - 'a')] = 1;
      ex[(second[(i + 1)] - 'a')] = 1;
    }
  }
  for (int i = 0; i < 26; i++) {
    if (pa[i] != -1) {
      adj[i].push_back(pa[i]);
    }
  }
  for (int i = 0; i < 26; i++) {
    if (ex[i] && co[i] == 0) {
      dfs(i);
    }
  }
  if (che) {
    cout << "NO";
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < 26; j++) {
      if (i != j && pa[i] != -1 && pa[i] == pa[j]) {
        cout << "NO";
        return 0;
      }
    }
  }
  bool iso[26];
  for (int i = 0; i < 26; i++) {
    iso[i] = 0;
  }
  for (int i = 0; i < 26; i++) {
    if (pa[i] != -1) {
      iso[pa[i]] = 1;
    }
  }
  vector<int> vec;
  for (int i = 0; i < 26; i++) {
    if (ex[i] && iso[i] == 0) {
      vec.push_back(i);
    }
  }
  sort(vec.begin(), vec.end());
  for (auto u : vec) {
    int node = u;
    while (node != -1) {
      cout << char('a' + node);
      node = pa[node];
    }
  }
  return 0;
}
