Problem:
Score : 200 points

Problem Statement

You have a digit sequence S of length 4. You are wondering which of the following formats S is in:

YYMM format: the last two digits of the year and the two-digit representation of the month (example: 01 for January), concatenated in this order

MMYY format: the two-digit representation of the month and the last two digits of the year, concatenated in this order

If S is valid in only YYMM format, print YYMM; if S is valid in only MMYY format, print MMYY; if S is valid in both formats, print AMBIGUOUS; if S is valid in neither format, print NA.

Constraints

S is a digit sequence of length 4.

Input

Input is given from Standard Input in the following format:

S

Output

Print the specified string: YYMM, MMYY, AMBIGUOUS or NA.

Sample Input 1

1905

Sample Output 1

YYMM

May XX19 is a valid date, but 19 is not valid as a month. Thus, this string is only valid in YYMM format.

Sample Input 2

0112

Sample Output 2

AMBIGUOUS

Both December XX01 and January XX12 are valid dates. Thus, this string is valid in both formats.

Sample Input 3

1700

Sample Output 3

NA

Neither 0 nor 17 is valid as a month. Thus, this string is valid in neither format.

Solution in C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace KyoPro
{
    class Program
    {
        static void Main(string[] args)
        {
            string S = Console.ReadLine();

            string first = S.Substring(0, 2);
            string last = S.Substring(2, 2);

            if (IsYearString(first))
            {
                if (IsYearString(last))
                {
                    Console.WriteLine("NA");
                }
                else
                {
                    Console.WriteLine("YYMM");
                }
            }
            else if (IsYearString(last))
            {
                Console.WriteLine("MMYY");
            }
            else
            {
                Console.WriteLine("AMBIGUOUS");
            }
        }

        static bool IsYearString(string s)
        {
            char first = s[0];
            char last = s[1];

            if (first != '0' && first != '1')
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }
}