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;
bool b[200000][26];
string mrg(string a, string b) {
  int fi = -1;
  for (int j = 0; j < a.length(); j++) {
    int l = min(b.length(), a.length() - j);
    if (a.substr(j, l) == b.substr(0, l)) {
      fi = j;
      break;
    }
  }
  if (fi == -1) {
    swap(a, b);
    for (int j = 0; j < a.length(); j++) {
      int l = min(b.length(), a.length() - j);
      if (a.substr(j, l) == b.substr(0, l)) {
        fi = j;
        break;
      }
    }
  }
  if (fi == -1) {
    cout << "NO" << endl;
    exit(0);
  }
  if (fi + b.length() <= a.length()) return a;
  return a.substr(0, fi) + b;
}
int main() {
  cin.sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  string s[2 * n];
  for (int i = 0; i < n; i++) cin >> s[i];
  for (int i = 0; i < n; i++) {
    if (s[i].length() > 26) {
      cout << "NO" << endl;
      return 0;
    }
    for (int x = 0; x < s[i].length(); x++) {
      for (int j = x + 1; j < s[i].length(); j++) {
        if (s[i][x] == s[i][j]) {
          cout << "NO" << endl;
          return 0;
        }
      }
    }
    for (char c : s[i]) b[i][c - 'a'] = 1;
  }
  set<int> q;
  int iter = n;
  for (int i = 0; i < n; i++) {
    string tp = s[i];
    set<int> p = q;
    for (int j : p) {
      for (char c : s[i]) {
        if (b[j][c - 'a']) {
          tp = mrg(tp, s[j]);
          q.erase(q.find(j));
          break;
        }
      }
    }
    if (tp != s[i]) {
      s[iter] = tp;
      if (s[iter].length() > 26) {
        cout << "NO" << endl;
        return 0;
      }
      for (int x = 0; x < s[iter].length(); x++) {
        for (int j = x + 1; j < s[iter].length(); j++) {
          if (s[iter][x] == s[iter][j]) {
            cout << "NO" << endl;
            return 0;
          }
        }
      }
      for (char c : s[iter]) b[iter][c - 'a'] = 1;
      q.insert(iter);
      iter++;
    } else {
      q.insert(i);
    }
  }
  string cp[q.size()];
  int qo = 0;
  for (int i : q) cp[qo++] = s[i];
  int sz = q.size();
  for (int i = 0; i < sz; i++) {
    s[i] = cp[i];
  }
  sort(s, s + sz);
  string ans = "";
  for (int i = 0; i < sz; i++) {
    int fi = -1;
    for (int j = 0; j < ans.length(); j++) {
      int l = min(s[i].length(), ans.length() - j);
      if (ans.substr(j, l) == s[i].substr(0, l)) {
        fi = j;
        break;
      }
    }
    if (fi == -1)
      ans += s[i];
    else {
      if (fi + s[i].length() <= ans.length())
        continue;
      else
        ans = ans.substr(0, fi) + s[i];
    }
    if (ans.length() > 26) break;
  }
  cout << ans << endl;
}
