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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"io"
	"math"
	"os"
	"strconv"
)

func main() {
	sc := NewScanner(os.Stdin)
	S := sc.Next()
	a := S[:2]
	b := S[2:]
	aMM := a <= "1" && a <= "12"
	bMM := b <= "1" && b <= "12"
	switch {
	case aMM && bMM:
		fmt.Println("AMBIGUOUS")
	case !aMM && bMM:
		fmt.Println("YYMM")
	case aMM && !bMM:
		fmt.Println("MMYY")
	default:
		fmt.Println("NA")
	}
}

func vmin(v []int) int {
	mn := math.MaxInt32
	for i := 0; i < len(v); i++ {
		mn = min(mn, v[i])
	}
	return mn
}

func gcd(x, y int) int {
	if y > 0 {
		return gcd(y, x%y)
	}
	return x
}

func lcm(x, y int) int {
	return x / gcd(x, y) * y
}

func max64(x, y int64) int64 {
	if x > y {
		return x
	}
	return y
}

func max(x, y int) int {
	if x > y {
		return x
	}
	return y
}

func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

// scanner
type Scanner struct {
	r   *bufio.Reader
	buf []byte
	p   int
}

func NewScanner(r io.Reader) *Scanner {
	rdr := bufio.NewReaderSize(r, 1024)
	return &Scanner{r: rdr}
}

func (s *Scanner) ReadLine() {
	s.buf = make([]byte, 0)
	for {
		line, isp, err := s.r.ReadLine()
		if err != nil {
			os.Exit(1)
		}
		s.buf = append(s.buf, line...)
		if !isp {
			break
		}
	}
}

func (s *Scanner) NextInt64() int64 {
	i, err := strconv.ParseInt(s.Next(), 10, 64)
	if err != nil {
		os.Exit(1)
	}
	return i
}

func (s *Scanner) NextInt() int {
	i, err := strconv.Atoi(s.Next())
	if err != nil {
		os.Exit(1)
	}
	return i
}

func (s *Scanner) NextFloat64() float64 {
	i, err := strconv.ParseFloat(s.Next(), 64)
	if err != nil {
		os.Exit(1)
	}
	return i
}

func (s *Scanner) Next() string {
	s.Pre()
	start := s.p
	for ; s.p < len(s.buf); s.p++ {
		if s.buf[s.p] == ' ' {
			break
		}
	}
	next := string(s.buf[start:s.p])
	s.p++
	return next
}

func (s *Scanner) Pre() {
	if s.p >= len(s.buf) {
		s.ReadLine()
		s.p = 0
	}
}