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 N = 100000 + 10;
char s[N];
int n, mp[1002][1002], in[1002], out[1002], nxt[1002], vis[1002], vis2[1002];
set<int> st;
vector<int> v[1002];
string str[1002];
bool cmp(string s1, string s2) { return (s1 + s2) < (s2 + s1); }
int main() {
  scanf("%d", &n);
  bool flag = 1;
  for (int i = 1; i <= n; i++) {
    scanf("%s", s + 1);
    st.clear();
    int len = strlen(s + 1);
    for (int pos = 1; pos <= len; pos++) {
      vis[s[pos]] = 1;
      st.insert(s[pos]);
      if (pos < len) mp[s[pos]][s[pos + 1]] = 1;
    }
    if (st.size() != len) flag = 0;
  }
  for (int i = 'a'; i <= 'z'; i++) {
    for (int j = 'a'; j <= 'z'; j++) {
      if (mp[i][j]) {
        v[i].push_back(j);
        in[j]++;
        out[i]++;
      }
    }
  }
  for (int i = 'a'; i <= 'z'; i++) {
    if (in[i] >= 2 || out[i] >= 2) flag = 0;
  }
  if (!flag) {
    printf("NO\n");
    return 0;
  }
  int cnt = 1;
  vector<int> start;
  for (int i = 'a'; i <= 'z'; i++) {
    if (in[i] == 0 && out[i] == 0 && vis[i]) {
      start.push_back(i);
    }
    if (in[i] == 0 && out[i] == 1) {
      start.push_back(i);
    }
  }
  for (int i = 0; i < start.size(); i++) {
    int cur = start[i];
    str[cnt] = "";
    str[cnt] = str[cnt] + (char)cur;
    vis2[cur] = 1;
    while (out[cur]) {
      out[cur]--;
      cur = v[cur][0];
      str[cnt] += cur;
      vis2[cur] = 1;
    }
    cnt++;
  }
  for (int i = 'a'; i <= 'z'; i++) {
    if (vis[i] == 1 && vis2[i] == 0) {
      printf("NO\n");
      return 0;
    }
  }
  sort(str + 1, str + cnt, cmp);
  for (int i = 1; i < cnt; i++) {
    cout << str[i];
  }
}
