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 {

    public static void main(String[] args) throws Exception {
        MyReader reader = new MyReader(System.in);
        MyWriter writer = new MyWriter(System.out);
        new Solution().run(reader, writer);
        writer.close();
    }

    private void run(MyReader reader, MyWriter writer) throws IOException {
        int n = reader.nextInt();
        List<String> list = new ArrayList<>();
        List<Boolean> b = new ArrayList<>();
        List<Set<Character>> set = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(reader.nextString());
            b.add(true);
        }
        list.sort((e1, e2) -> e2.length() - e1.length());
        for (int i = 0; i < n; i++) {
            set.add(new HashSet<>());
            for (char c : list.get(i).toCharArray()) {
                if (!set.get(i).add(c)) {
                    writer.print("NO");
                    return;
                }
            }
        }
        for (int i = 0; i < list.size(); i++) {
            if (!b.get(i)) {
                continue;
            }
            boolean y = true;
            while (y) {
                y = false;
                for (int j = i + 1; j < list.size(); j++) {
                    if (b.get(j)) {
                        int e = 0;
                        for (char c : set.get(j)) {
                            if (set.get(i).contains(c)) {
                                e++;
                            }
                        }
                        if (e > 0) {
                            if (e == list.get(j).length()) {
                                if (list.get(i).contains(list.get(j))) {
                                    b.set(j, false);
                                } else {
                                    writer.print("NO");
                                    return;
                                }
                            } else {
                                String s;
                                if (list.get(i).endsWith(list.get(j).substring(0, e))) {
                                    s = list.get(i) + list.get(j).substring(e);
                                } else if (list.get(j).endsWith(list.get(i).substring(0, e))) {
                                    s = list.get(j) + list.get(i).substring(e);
                                } else {
                                    writer.print("NO");
                                    return;
                                }
                                Set<Character> se = new HashSet<>();
                                for (char c : s.toCharArray()) {
                                    se.add(c);
                                }
                                list.set(i, s);
                                set.set(i, se);
                                list.remove(j);
                                set.remove(j);
                                b.remove(j);
                                j--;
                                y = true;
                            }
                        }
                    }
                }
            }
        }
        List<String> list1 = new ArrayList<>();
        for (int i = 0; i < list.size(); i++) {
            if (b.get(i)) {
                list1.add(list.get(i));
            }
        }
        list1.sort(Comparator.naturalOrder());
        for (String s : list1) {
            writer.print(s);
        }
    }

    static class MyReader {

        final BufferedInputStream in;
        final int bufSize = 1 << 16;
        final byte buf[] = new byte[bufSize];
        int i = bufSize;
        int k = bufSize;
        final StringBuilder str = new StringBuilder();

        MyReader(InputStream in) {
            this.in = new BufferedInputStream(in, bufSize);
        }

        int nextInt() throws IOException {
            return (int) nextLong();
        }

        int[] nextIntArray(int n) throws IOException {
            int[] m = new int[n];
            for (int i = 0; i < n; i++) {
                m[i] = nextInt();
            }
            return m;
        }

        int[][] nextIntMatrix(int n, int m) throws IOException {
            int[][] a = new int[n][0];
            for (int j = 0; j < n; j++) {
                a[j] = nextIntArray(m);
            }
            return a;
        }

        long nextLong() throws IOException {
            int c;
            long x = 0;
            boolean sign = true;
            while ((c = nextChar()) <= 32) ;
            if (c == '-') {
                sign = false;
                c = nextChar();
            }
            if (c == '+') {
                c = nextChar();
            }
            while (c >= '0') {
                x = x * 10 + (c - '0');
                c = nextChar();
            }
            return sign ? x : -x;
        }

        long[] nextLongArray(int n) throws IOException {
            long[] m = new long[n];
            for (int i = 0; i < n; i++) {
                m[i] = nextLong();
            }
            return m;
        }

        int nextChar() throws IOException {
            if (i == k) {
                k = in.read(buf, 0, bufSize);
                i = 0;
            }
            return i >= k ? -1 : buf[i++];
        }

        String nextString() throws IOException {
            int c;
            str.setLength(0);
            while ((c = nextChar()) <= 32 && c != -1) ;
            if (c == -1) {
                return null;
            }
            while (c > 32) {
                str.append((char) c);
                c = nextChar();
            }
            return str.toString();
        }

        String nextLine() throws IOException {
            int c;
            str.setLength(0);
            while ((c = nextChar()) <= 32 && c != -1) ;
            if (c == -1) {
                return null;
            }
            while (c != '\n') {
                str.append((char) c);
                c = nextChar();
            }
            return str.toString();
        }

        char[] nextCharArray() throws IOException {
            return nextString().toCharArray();
        }

        char[][] nextCharMatrix(int n) throws IOException {
            char[][] a = new char[n][0];
            for (int i = 0; i < n; i++) {
                a[i] = nextCharArray();
            }
            return a;
        }
    }

    static class MyWriter {

        final BufferedOutputStream out;
        final int bufSize = 1 << 16;
        final byte buf[] = new byte[bufSize];
        int i = 0;
        final byte c[] = new byte[30];
        static final String newLine = System.getProperty("line.separator");

        MyWriter(OutputStream out) {
            this.out = new BufferedOutputStream(out, bufSize);
        }

        void print(long x) throws IOException {
            int j = 0;
            if (i + 30 >= bufSize) {
                flush();
            }
            if (x < 0) {
                buf[i++] = (byte) ('-');
                x = -x;
            }
            while (j == 0 || x != 0) {
                c[j++] = (byte) (x % 10 + '0');
                x /= 10;
            }
            while (j-- > 0)
                buf[i++] = c[j];
        }

        void print(int[] m) throws IOException {
            for (int a : m) {
                print(a);
                print(' ');
            }
        }

        void print(long[] m) throws IOException {
            for (long a : m) {
                print(a);
                print(' ');
            }
        }

        void print(String s) throws IOException {
            for (int i = 0; i < s.length(); i++) {
                print(s.charAt(i));
            }
        }

        void print(char x) throws IOException {
            if (i == bufSize) {
                flush();
            }
            buf[i++] = (byte) x;
        }

        void print(char[] m) throws IOException {
            for (char c : m) {
                print(c);
            }
        }

        void println(String s) throws IOException {
            print(s);
            println();
        }

        void println() throws IOException {
            print(newLine);
        }

        void flush() throws IOException {
            out.write(buf, 0, i);
            out.flush();
            i = 0;
        }

        void close() throws IOException {
            flush();
            out.close();
        }
    }
}