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 double pi =
    3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342;
const int MR = 500;
const int MS = 1e5 + 10;
set<char> g[MR];
bool done[MR], present[MR];
int inDeg[MR];
char s[MS];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < (n); ++i) {
    scanf("%s", s);
    int dl = strlen(s);
    for (int i = 0; i < (dl - 1); ++i)
      if (g[s[i]].insert(s[i + 1]).second) inDeg[s[i + 1]]++;
    for (int i = 0; i < (dl); ++i) present[s[i]] = 1;
  }
  string res = "";
  int ilep = 0;
  for (int c = ('a'); c <= ('z'); ++c) {
    ilep += present[c];
    if (inDeg[c] > 1) {
      printf("NO\n");
      return 0;
    }
  }
  char st = '#';
  while (res.length() < ilep) {
    if (st == '#') {
      for (int c = ('a'); c <= ('z'); ++c)
        if (present[c] && !inDeg[c] && !done[c]) {
          st = c;
          break;
        }
    }
    if (st == '#') {
      printf("NO\n");
      return 0;
    }
    res += st;
    done[st] = 1;
    if (g[st].size() > 1) {
      printf("NO\n");
      return 0;
    }
    if (g[st].empty()) st = '#';
    for (char c : g[st]) {
      inDeg[c]--;
      if (!inDeg[c]) st = c;
    }
  }
  printf("%s\n", res.c_str());
  return 0;
}
