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>
#pragma GCC optimize(3)
using namespace std;
bool Finish_read;
template <class T>
inline void read(T &x) {
  Finish_read = 0;
  x = 0;
  int f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    if (ch == EOF) return;
    ch = getchar();
  }
  while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
  x *= f;
  Finish_read = 1;
}
template <class T>
inline void print(T x) {
  if (x / 10 != 0) print(x / 10);
  putchar(x % 10 + '0');
}
template <class T>
inline void writeln(T x) {
  if (x < 0) putchar('-');
  x = abs(x);
  print(x);
  putchar('\n');
}
template <class T>
inline void write(T x) {
  if (x < 0) putchar('-');
  x = abs(x);
  print(x);
}
const int maxn = 100010;
string s[maxn];
int n, len[maxn], suf[26], pre[26], ans[26], fst, cnt;
bool vis[maxn], have[26], appear[26];
int main() {
  memset(pre, -1, sizeof pre);
  memset(suf, -1, sizeof suf);
  read(n);
  bool err = 0;
  for (int i = 1; i <= n; i++) {
    cin >> s[i];
    memset(have, 0, sizeof have);
    for (int j = 0; j < s[i].length(); j++) {
      if (have[s[i][j] - 'a']) {
        err = 1;
        break;
      }
      have[s[i][j] - 'a'] = 1;
      appear[s[i][j] - 'a'] = 1;
    }
  }
  if (err) {
    puts("NO");
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    len[i] = s[i].length();
    for (int j = 0; j < len[i] - 1; j++) {
      if (suf[s[i][j] - 'a'] != -1) {
        if (s[i][j + 1] - 'a' != suf[s[i][j] - 'a']) {
          err = 1;
          break;
        }
      } else {
        suf[s[i][j] - 'a'] = s[i][j + 1] - 'a';
        pre[s[i][j + 1] - 'a'] = s[i][j] - 'a';
      }
    }
    if (err) break;
  }
  if (err) {
    puts("NO");
    return 0;
  }
  memset(vis, 0, sizeof vis);
  bool ou = 0;
  for (int i = 0; i < 26; i++) {
    if (pre[i] == -1 && appear[i]) {
      ou = 1;
      fst = i;
      while (fst != -1) {
        if (vis[fst]) {
          puts("NO");
          return 0;
        }
        ans[++cnt] = fst;
        vis[fst] = 1;
        fst = suf[fst];
      }
    }
  }
  for (int i = 0; i < 26; i++)
    if (appear[i] && !vis[i]) ou = 0;
  if (!ou) {
    puts("NO");
    return 0;
  }
  for (int i = 1; i <= cnt; i++) putchar(ans[i] + 'a');
}
