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 maxn = 100011;
string s[maxn];
int n;
void init() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) cin >> s[i];
}
int w[maxn][27];
bool b[maxn];
inline bool cmp_s(int x, int y) { return s[x] < s[y]; }
void work() {
  memset(w, 255, sizeof(w));
  for (int i = 1; i <= n; ++i) {
    if (s[i].size() > 26) return puts("NO"), void();
    for (unsigned j = 0; j < s[i].size(); ++j)
      if (~w[i][s[i][j] - 'a'])
        return puts("NO"), void();
      else
        w[i][s[i][j] - 'a'] = j;
  }
  for (int c = 0; c < 26; ++c) {
    int t = 0;
    bool ok = 0;
    string S = "";
    S += 'a' + c;
    for (int i = 1; i <= n; ++i)
      if (!b[i] && ~w[i][c]) {
        for (int j = 0; t + j < S.size() && w[i][c] + j < s[i].size(); ++j)
          if (S[t + j] != s[i][w[i][c] + j]) return puts("NO"), void();
        for (int j = 0; t - j >= 0 && w[i][c] - j >= 0; ++j)
          if (S[t - j] != s[i][w[i][c] - j]) return puts("NO"), void();
        for (unsigned j = w[i][c] + S.size() - t; j < s[i].size(); ++j)
          S += s[i][j];
        for (int j = w[i][c] - t - 1; j >= 0; --j)
          S = string(1, s[i][j]) + S, ++t;
        b[i] = 1;
        ok = 1;
      }
    if (ok) {
      s[++n] = S;
      for (unsigned j = 0; j < s[n].size(); ++j)
        if (~w[n][s[n][j] - 'a'])
          return puts("NO"), void();
        else
          w[n][s[n][j] - 'a'] = j;
    }
  }
  static int w[maxn];
  for (int i = 1; i <= n; ++i) w[i] = i;
  sort(w + 1, w + n + 1, cmp_s);
  for (int i = 1; i <= n; ++i)
    if (!b[w[i]]) cout << s[w[i]];
  cout << endl;
}
int main() {
  init();
  work();
  return 0;
}
