Problem:
Score : 300 points

Problem Statement

There is a grid with infinitely many rows and columns. In this grid, there is a rectangular region with consecutive N rows and M columns, and a card is placed in each square in this region.
The front and back sides of these cards can be distinguished, and initially every card faces up.

We will perform the following operation once for each square contains a card:

For each of the following nine squares, flip the card in it if it exists: the target square itself and the eight squares that shares a corner or a side with the target square.

It can be proved that, whether each card faces up or down after all the operations does not depend on the order the operations are performed.
Find the number of cards that face down after all the operations.

Constraints

1 \leq N,M \leq 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N M

Output

Print the number of cards that face down after all the operations.

Sample Input 1

2 2

Sample Output 1

0

We will flip every card in any of the four operations. Thus, after all the operations, all cards face up.

Sample Input 2

1 7

Sample Output 2

5

After all the operations, all cards except at both ends face down.

Sample Input 3

314 1592

Sample Output 3

496080

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"reflect"
	"sort"
	"strconv"
	"strings"
	// "regexp"
)

/* sort */
type pair struct {
	index  int64
	p1, p2 interface{}
}
type pairs []pair

func (slice pairs) Len() int {
	return len(slice)
}

func (slice pairs) Less(i, j int) bool {
	return slice[i].index < slice[j].index
}

func (slice pairs) Swap(i, j int) {
	slice[i], slice[j] = slice[j], slice[i]
}

/* sort */
type Int64Slice []int64

func (slice Int64Slice) Len() int {
	return len(slice)
}

func (slice Int64Slice) Less(i, j int) bool {
	return slice[i] < slice[j]
}

func (slice Int64Slice) Swap(i, j int) {
	slice[i], slice[j] = slice[j], slice[i]
}
func Int64s(a []int64)                    { sort.Sort(Int64Slice(a)) }
func Int64sSliceAreSorted(a []int64) bool { return sort.IsSorted(Int64Slice(a)) }

const (
	initialBufSize = 1e4
	maxBufSize     = 1e8
	INF            = 1e8
)

var (
	scanner = bufio.NewScanner(os.Stdin)
	writer  = bufio.NewWriter(os.Stdout)
	di      = []int64{-1, 0, 1, 0}
	dj      = []int64{0, -1, 0, 1}
)

func main() {
	buf := make([]byte, initialBufSize)
	scanner.Buffer(buf, maxBufSize)
	scanner.Split(bufio.ScanWords)
	N, M := readInt(), readInt()
	ans := int64(0)
	if N == 1 || M == 1 {
		if N == 1 && M > 1 {
			ans += M - 2
		}
		if M == 1 && N > 1 {
			ans += N - 2
		}
		if N == 1 && M == 1 {
			ans += 1
		}
	} else if N > 2 && M > 2 {
		ans += (N - 2) * (M - 2)
	}
	fmt.Println(ans)
}

/*==========================================
 *             Library
 *==========================================*/
func NextPermutation(x sort.Interface) bool {
	n := x.Len() - 1
	if n < 1 {
		return false
	}
	j := n - 1
	for ; !x.Less(j, j+1); j-- {
		if j == 0 {
			return false
		}
	}
	l := n
	for !x.Less(j, l) {
		l--
	}
	x.Swap(j, l)
	for k, l := j+1, n; k < l; {
		x.Swap(k, l)
		k++
		l--
	}
	return true
}
func doubleAry(h int64, w int64, init int64) (res [][]int64) {
	res = make([][]int64, h)
	for i := int64(0); i < h; i++ {
		res[i] = make([]int64, w)
		for j := int64(0); j < w; j++ {
			res[i][j] = init
		}
	}
	return
}

func aryEq(a []int64, b []int64) bool {
	return reflect.DeepEqual(a, b)
}

func clone(n []int64) (r []int64) {
	r = make([]int64, len(n))
	for i := 0; i < len(n); i++ {
		r[i] = n[i]
	}
	return
}
func write(s string) {
	writer.WriteString(s)
}

func print() {
	writer.Flush()
}

// scanner.Split(bufio.ScanWords) をコメントアウトしないと使用不可
func readLine() (s string) {
	if scanner.Scan() {
		s = scanner.Text()
	}
	return s
}

func readInt() (read int64) {
	scanner.Scan()
	read, err := strconv.ParseInt(scanner.Text(), 10, 64)
	if err != nil {
		panic(err)
	}
	return
}

func readFloat() (read float64) {
	scanner.Scan()
	read, err := strconv.ParseFloat(scanner.Text(), 64)
	if err != nil {
		panic(err)
	}
	return
}

func readRunes() (read []rune) {
	scanner.Scan()
	for _, v := range scanner.Text() {
		read = append(read, v)
	}
	return
}

func readString() (read string) {
	scanner.Scan()
	read = scanner.Text()
	return
}

func readStrings() (read []string) {
	scanner.Scan()
	for _, v := range scanner.Text() {
		read = append(read, string(v))
	}
	return
}

func s2i(s string) int64 {
	var intVal, e = strconv.ParseInt(s, 10, 64)
	if e != nil {
		panic(e)
	}
	return intVal
}

func i2s(i int64) string {
	var strVal = strconv.FormatInt(i, 10)
	return strVal
}

func s2f(s string) float64 {
	var floatVal, e = strconv.ParseFloat(s, 64)
	if e != nil {
		panic(e)
	}
	return floatVal
}

func abs(i int64) int64 {
	return int64(math.Abs(float64(i)))
}

func max(a ...int64) int64 {
	ans := int64(0)
	for i, v := range a {
		if i == 0 {
			ans = v
		}
		if ans < v {
			ans = v
		}
	}
	return ans
}
func min(a ...int64) int64 {
	ans := int64(0)
	for i, v := range a {
		if i == 0 {
			ans = v
		}
		if ans > v {
			ans = v
		}
	}
	return ans
}

func sum(i []int64) int64 {
	sum := int64(0)
	for _, val := range i {
		sum += val
	}
	return sum
}

func split(s string) []string {
	return strings.Fields(s)
}

func strAry2intAry(strs []string) []int64 {
	var ret = make([]int64, 0, len(strs))
	for _, str := range strs {
		var intVal = s2i(str)
		ret = append(ret, intVal)
	}
	return ret
}

func intAry2strAry(nums []int64) []string {
	var ret = make([]string, 0, len(nums))
	for _, num := range nums {
		var strVal = i2s(num)
		ret = append(ret, strVal)
	}
	return ret
}

func ary2str(strs []string) string {
	return strings.Join(strs, " ")
}

func reverse(res []int64) []int64 {
	for i, j := 0, len(res)-1; i < j; i, j = i+1, j-1 {
		res[i], res[j] = res[j], res[i]
	}
	return res
}
func reverseStr(res []string) []string {
	for i, j := 0, len(res)-1; i < j; i, j = i+1, j-1 {
		res[i], res[j] = res[j], res[i]
	}
	return res
}

func ini(res []int, init int) {
	if len(res) == 0 {
		return
	}
	res[0] = init
	for i := 0; i < len(res); i++ {
		copy(res[i:], res[:i])
	}
}

//
// func regexpExample() {
//     // Your code here!
//     var str = "13:20"
//     r := regexp.MustCompile(`(\d+):(\d+)`)
//     fmt.Println(r.FindStringSubmatch(str))
// }

// type Country struct {
//     gold int
//     silver int
//     blonze int
// }

// // 複数ソートのサンプル
// func stableSortExample() []Country{
//     var country = []Country {
//         {gold:1, silver:2, blonze:3},
//         {gold:1, silver:2, blonze:3},
//         {gold:1, silver:3, blonze:2},
//         {gold:1, silver:3, blonze:3},
//     }
//     sort.SliceStable(country, func(i, j int) bool { return country[i].blonze > country[j].blonze })
//     sort.SliceStable(country, func(i, j int) bool { return country[i].silver > country[j].silver })
//     sort.SliceStable(country, func(i, j int) bool { return country[i].gold > country[j].gold })
//     return country
// }