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;
int n;
vector<int> rt[256];
vector<int> brt[256];
bool e[256];
string ss[101010];
vector<string> co;
bool ok;
string get(char c) {
  string rv = "a";
  rv[0] = c;
  if (!e[c]) return "";
  e[c] = 0;
  if (rt[c].size())
    return rv + get(rt[c][0]);
  else
    return rv;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> ss[i];
    for (int j = 0; j < ss[i].size(); ++j) e[ss[i][j]] = 1;
    for (int j = 0; j + 1 < ss[i].size(); ++j) {
      rt[ss[i][j]].push_back(ss[i][j + 1]);
      brt[ss[i][j + 1]].push_back(ss[i][j]);
    }
  }
  ok = 1;
  for (int c = 'a'; c <= 'z'; ++c) {
    for (int i = 0; i < rt[c].size(); ++i)
      if (rt[c][i] != rt[c][0]) ok = 0;
    for (int i = 0; i < brt[c].size(); ++i)
      if (brt[c][i] != brt[c][0]) ok = 0;
  }
  string cs = "";
  for (int c = 'a'; c <= 'z'; ++c) {
    if (brt[c].size() == 0) co.push_back(get(c));
  }
  for (int c = 'a'; c <= 'z'; ++c)
    if (e[c]) ok = 0;
  if (!ok)
    cout << "NO\n";
  else {
    sort(co.begin(), co.end());
    for (auto t : co) cout << t;
    cout << "\n";
  }
}
