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 MOD = 1000000007;
const int UNDEF = -1;
const long long INF = 1e18;
template <typename T>
inline bool chkmax(T &aa, T bb) {
  return aa < bb ? aa = bb, true : false;
}
template <typename T>
inline bool chkmin(T &aa, T bb) {
  return aa > bb ? aa = bb, true : false;
}
const int mn = 1e5 + 4;
string a[mn];
int al[mn];
set<char> gin[256], gout[256];
bool seen[256];
int n;
string ans;
void fail() {
  printf("NO\n");
  exit(0);
}
void dfs(char c) {
  if (seen[c]) fail();
  seen[c] = true;
  ans += c;
  if (gout[c].size() >= 2) fail();
  if (gout[c].size() == 1) dfs(*(gout[c].begin()));
}
bool occ[256];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n;
  for (int x = 0; x < n; x++) {
    cin >> a[x];
    al[x] = a[x].length();
    for (auto &c : a[x]) {
      occ[c] = true;
    }
    for (int p = 1; p < al[x]; p++) {
      char c1 = a[x][p - 1];
      char c2 = a[x][p];
      gout[c1].insert(c2);
      gin[c2].insert(c1);
    }
  }
  for (int c = 'a'; c <= 'z'; c++) {
    if (gin[c].size() >= 2 || gout[c].size() >= 2) fail();
  }
  for (int c = 'a'; c <= 'z'; c++) {
    if (gin[c].size() == 0 && occ[c]) {
      dfs(c);
    }
  }
  if (ans.size() >= 50) fail();
  for (int x = 0; x < n; x++) {
    if (string::npos == ans.find(a[x])) fail();
  }
  cout << ans << "\n";
}
