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.
import java.io.*;
import java.util.*;

public class __Solution {

    static final boolean ONLINE_JUDGE = System.getProperty("ONLINE_JUDGE") != null;

    public static void main(String[] args) {
        new __Solution().run();
    }

    BufferedReader in;
    PrintWriter out;
    StringTokenizer tok;

    void init() throws FileNotFoundException {

        if (ONLINE_JUDGE) {
            in = new BufferedReader(new InputStreamReader(System.in));
            out = new PrintWriter(System.out);
        } else {
            in = new BufferedReader(new FileReader("input.txt"));
            out = new PrintWriter("output.txt");
        }

        tok = new StringTokenizer("");
    }

    void run() {
        try {
            long timeStart = System.currentTimeMillis();

            init();
            solve();

            out.close();

            long timeEnd = System.currentTimeMillis();
            System.err.println("Time = " + (timeEnd - timeStart));
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(-1);
        }
    }

    String readLine() throws IOException {
        return in.readLine();
    }

    String delimiter = " ";

    String readString() throws IOException {
        while (!tok.hasMoreTokens()) {
            String nextLine = readLine();
            if (null == nextLine) return null;

            tok = new StringTokenizer(nextLine);
        }

        return tok.nextToken(delimiter);
    }

    int readInt() throws IOException {
        return Integer.parseInt(readString());
    }

    long readLong() throws IOException {
        return Long.parseLong(readString());
    }

    void solve() throws IOException {
        int[] input = new int[26];
        int[] output = new int[26];
        boolean[] was = new boolean[26];
        Arrays.fill(input, -1);
        Arrays.fill(output, -1);
        Arrays.fill(was, false);

        int n = readInt();
        for (int i = 0; i < n; i++) {
            char[] string = readString().toCharArray();
            for (int j = 0; j < string.length; j++)
                was[string[j]-'a'] = true;
            for (int j = 0; j < string.length-1; j++) {
                int n1 = string[j]-'a';
                int n2 = string[j+1]-'a';
                if (n2 == n1) {
                    out.println("NO");
                    return;
                }
                if (output[n1] != -1 && output[n1] != n2) {
                    out.println("NO");
                    return;
                }
                output[n1] = n2;
                if (input[n2] != -1 && input[n2] != n1) {
                    out.println("NO");
                    return;
                }
                input[n2] = n1;
            }
        }
        boolean h = true;
        String ans = "";
        for (int i = 0; i < 26; i++) {
            if (was[i] && input[i] == -1) {
                h = false;
                int now = i;
                while (now != -1) {
                    was[now] = false;
                    ans += (char)(((char)now)+'a');
                    now = output[now];
                }
            }
        }
        for (int i = 0; i < 26; i++)
            if (was[i])
            {
                out.println("NO");
                return;
            }
        if (h)
            out.print("NO");
        out.print(ans);
    }
}