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 = 3000000;
const int MOD = 1e9 + 7;
const int C = 26;
int n;
int cnext[C], cprev[C];
int degIn[C], degOut[C];
int status[C];
bool used[C];
bool flag;
string ans;
void dfs(int v) {
  status[v] = 1;
  if (cnext[v] != -1) {
    if (status[cnext[v]] == 1) flag = false;
    if (status[cnext[v]] == 2) dfs(cnext[v]);
  }
  status[v] = 2;
}
void addEdge(int u, int v) {
  if (u == v) {
    flag = false;
    return;
  }
  if (cnext[u] != -1 && cnext[u] != v) {
    flag = false;
    return;
  }
  if (cprev[v] != -1 && cprev[v] != u) {
    flag = false;
    return;
  }
  degIn[v]++;
  cnext[u] = v;
  cprev[v] = u;
}
int main() {
  cin >> n;
  memset(cnext, -1, sizeof(cnext));
  memset(cprev, -1, sizeof(cprev));
  memset(used, false, sizeof(used));
  flag = true;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    int m = s.length();
    for (int j = 0; j < m; j++) {
      used[s[j] - 'a'] = true;
    }
    for (int j = 0; j < m - 1; j++) {
      addEdge(s[j] - 'a', s[j + 1] - 'a');
    }
  }
  for (int i = 0; i < C; i++) {
    if (!status[i]) {
      dfs(i);
    }
  }
  if (flag) {
    ans = "";
    memset(status, 0, sizeof(status));
    for (int i = 0; i < C; i++) {
      if (!status[i] && used[i] && degIn[i] == 0) {
        int j = i;
        while (j != -1) {
          status[j] = 1;
          ans += j + 'a';
          j = cnext[j];
        }
      }
    }
    cout << ans;
  } else {
    cout << "NO";
  }
  return 0;
}
