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 db = long double;
using pll = pair<long long, long long>;
std::set<long long> g[27];
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t, i, x, j, y, z, k, n;
  set<long long> let;
  long long tt;
  cin >> tt;
  for (long long _tt = 0; _tt < tt; _tt++) {
    string s;
    cin >> s;
    n = s.size();
    for (auto zx : s) {
      let.insert(zx - 'a');
    }
    for (i = 1; i < n; i += 1) {
      j = s[i - 1] - 'a';
      k = s[i] - 'a';
      g[j].insert(k);
    }
  }
  string ans = "";
  bool br = false;
  long long used[27];
  for (i = 0; i < 27; i += 1) used[i] = 0;
  for (auto zx : let) {
    if (g[zx].size() > 1) br = true;
  }
  for (auto zx : let) {
    bool f = false;
    for (i = 0; i < 27; i += 1) {
      if (g[i].count(zx) > 0) f = true;
    }
    if (f || used[zx]) continue;
    i = zx;
    used[i] = 1;
    ans += char('a' + i);
    while (g[i].size()) {
      i = *g[i].begin();
      if (used[i]) {
        br = true;
        break;
      }
      used[i] = 1;
      ans += char('a' + i);
    }
  }
  for (auto zx : ans) {
    let.erase(zx - 'a');
  }
  if (let.size() || br || ans.size() == 0) ans = "NO";
  cout << ans << '\n';
}
