using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;

class Meguru
{

    public Meguru() { }
    public static int Main()
    {
        new Meguru().calc();
        return 0;
    }

    Scanner cin;

    void calc()
    {
        cin = new Scanner();
        int N = cin.nextInt();
        Dictionary<string, bool> dic = new Dictionary<string, bool>();
        for (int i = 0; i < N; i++)
        {
            dic[cin.next()] = true;
        }

        string[] ar1 = { "a", "a", "e", "i", "u", "u" };
        string[] ar2 = { "", "b", "g", "m", "n", "r" };

        do
        {
            do
            {
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < 6; i++)
                {
                    sb.Append(ar2[i]);
                    sb.Append(ar1[i]);
                }
                string s = sb.ToString();
                if (!dic.ContainsKey(s))
                {
                    Console.WriteLine(s);
                    return;
                }

            } while (next_permutation(ar2));
        } while (next_permutation(ar1));
        Console.WriteLine("NO");
    }

    //swap
    void swap<T>(ref T a, ref T b)
    {
        T c = a;
        a = b;
        b = c;
    }

    public static bool next_permutation<T>(T[] array) where T : IComparable<T>
    {
        return next_permutation(array, 0, array.Length);
    }

    public static bool next_permutation<T>(T[] array, int start, int length) where T : IComparable<T>
    {
        int end = start + length - 1;
        if (end <= start) return false;
        int last = end;
        while (true)
        {
            int pos = last--;
            if (array[last].CompareTo(array[pos]) < 0)
            {
                int i;
                for (i = end + 1; array[last].CompareTo(array[--i]) >= 0; ) { }
                T tmp = array[last]; array[last] = array[i]; array[i] = tmp;
                Array.Reverse(array, pos, end - pos + 1);
                return true;
            }
            if (last == start)
            {
                //Array.Reverse(array, start, end - start);
                return false;
            }
        }
    }
        

}






class Scanner
{
    string[] s;
    int i;

    char[] cs = new char[] { ' ' };

    public Scanner()
    {
        s = new string[0];
        i = 0;
    }

    public string next()
    {
        if (i < s.Length) return s[i++];
        string st = Console.ReadLine();
        while (st == "") st = Console.ReadLine();
        s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        i = 0;
        return next();
    }

    public int nextInt()
    {
        return int.Parse(next());
    }

    public long nextLong()
    {
        return long.Parse(next());
    }

    public double nextDouble()
    {
        return double.Parse(next());
    }

}