Problem:
﻿Score: 100 points

Problem Statement

There is a farm whose length and width are A yard and B yard, respectively. A farmer, John, made a vertical road and a horizontal road inside the farm from one border to another, as shown below: (The gray part represents the roads.)

What is the area of this yard excluding the roads? Find it.

Note

It can be proved that the positions of the roads do not affect the area.

Constraints

A is an integer between 2 and 100 (inclusive).

B is an integer between 2 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

A B

Output

Print the area of this yard excluding the roads (in square yards).

Sample Input 1

2 2

Sample Output 1

1

In this case, the area is 1 square yard.

Sample Input 2

5 7

Sample Output 2

24

In this case, the area is 24 square yards.

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

package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"math"
	"os"
	"strconv"
)

const (
	initialBufSize = 10000
	maxBufSize     = 1000000
	mod            = 1e9 + 7
)

var (
	sc *bufio.Scanner = func() *bufio.Scanner {
		sc := bufio.NewScanner(os.Stdin)
		buf := make([]byte, initialBufSize)
		sc.Buffer(buf, maxBufSize)
		sc.Split(bufio.ScanWords)
		return sc
	}()
)

func main() {
	A := getInt()
	B := getInt()

	fmt.Println(A * B - (A + B - 1))
}

type Graph struct {
	n     int
	edges [][]int
}

func NewGraph(n int) *Graph {
	g := &Graph{
		n:     n,
		edges: make([][]int, n),
	}
	return g
}

func (g *Graph) AddEdge(u, v int) {
	g.edges[v] = append(g.edges[v], u)
	g.edges[u] = append(g.edges[u], v)
}

func dfs(c int, edges [][]int, visited map[int]struct{}) {
	visited[c] = struct{}{}

	for _, v := range edges[c] {
		_, flag := visited[v]
		if flag {
			continue
		}
		dfs(v, edges, visited)
	}
}

func bfs(c int, graph *Graph) {
	next := make([]int, 0)
	next = append(next, c)
	visited := make(map[int]struct{})

	for ; len(next) != 0; {
		u := next[0]
		next = next[1:]
		visited[u] = struct{}{}

		for _, v := range graph.edges[u] {
			_, flag := visited[v]
			if flag {
				continue
			}

			// なにか処理

			next = append(next, v)
		}
	}
}

func getInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func getIntArray(n int) []int {
	array := make([]int, n)
	for i := 0; i < n; i++ {
		array[i] = getInt()
	}
	return array
}

func getString() string {
	sc.Scan()
	return sc.Text()
}

func abs(a int) int {
	return int(math.Abs(float64(a)))
}

func pow(p, q int) int {
	return int(math.Pow(float64(p), float64(q)))
}

func powMod(n, p int) int {
	if p == 0 {
		return 1
	} else if p%2 == 0 {
		t := powMod(n, p/2)
		return calcMod(t * t)
	} else {
		return calcMod(n * powMod(n, p-1))
	}
}

func min(nums ...int) int {
	if len(nums) == 0 {
		panic("funciton min() requires at least one argument.")
	}
	res := nums[0]
	for i := 0; i < len(nums); i++ {
		res = int(math.Min(float64(res), float64(nums[i])))
	}
	return res
}

func max(nums ...int) int {
	if len(nums) == 0 {
		panic("funciton max() requires at least one argument.")
	}
	res := nums[0]
	for i := 0; i < len(nums); i++ {
		res = int(math.Max(float64(res), float64(nums[i])))
	}
	return res
}

func strSearch(a []string, b string) bool {
	for i := 0; i < len(a); i++ {
		if a[i] == b {
			return true
		}
	}
	return false
}

func printIntArray(array []int) {
	strArray := fmt.Sprint(array)
	fmt.Println(strArray[1 : len(strArray)-1])
}

func calcMod(x int) int {
	return x % mod
}

func reverse(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}

func isPrime(n int) bool {
	if n < 2 {
		return false
	} else if n == 2 {
		return true
	} else if n % 2 == 0 {
		return false
	}

	sqrtN := int(math.Sqrt(float64(n)))
	for i := 3; i <= sqrtN; i += 2 {
		if n % i == 0 {
			return false
		}
	}

	return true
}

func contains(s []int, e int) bool {
	for _, v := range s {
		if e == v {
			return true
		}
	}
	return false
}

func makeRange(min, max int) []int {
	a := make([]int, max-min+1)
	for i := range a {
		a[i] = min + i
	}
	return a
}

func powerset2(nums []int) [][]int {
	length := int(math.Pow(2, float64(len(nums))))
	result := make([][]int, length)

	index := 0
	result[index] = []int{}
	index++

	for _, n := range nums {
		max := index
		for i := 0; i < max; i++ {
			result[index] = copyAndAppend(result[i], n)
			index++
		}
	}

	return result
}

func copyAndAppend(nums []int, n int) []int {
	dst := make([]int, len(nums)+1)
	copy(dst, nums)
	dst[len(nums)] = n
	return dst
}

func calcGcd(x, y int) int {
	if y == 0 {
		return x
	} else if x >= y {
		return calcGcd(y, x % y)
	} else {
		return calcGcd(x, y % x)
	}
}

func getDivisor(n int) []int {
	var divisor []int
	divisor = append(divisor, 1)
	if n != 1 {
		divisor = append(divisor, n)
	}

	sqrt := int(math.Sqrt(float64(n)))
	for i := 2; i <= sqrt; i++ {
		if n % i == 0 {
			divisor = append(divisor, i)
			divisor = append(divisor, n/i)
		}
	}
	return divisor
}

type intHeap []int

func (h intHeap) Len() int {
	return len(h)
}

func (h intHeap) Less(i, j int) bool {
	return h[i] > h[j]
}

func (h intHeap) Swap(i, j int) {
	h[i], h[j] = h[j], h[i]
}

func (h *intHeap) Push(x interface{}) {
	*h = append(*h, x.(int))
}

func (h *intHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

func initHeap() *intHeap {
	ih := &intHeap{}
	heap.Init(ih)
	return ih
}

func (h *intHeap) pushHeap(n int) {
	heap.Push(h, n)
}

func (h *intHeap) popHeap() int {
	return heap.Pop(h).(int)
}

func factMod(n int) int {
	value := 1
	for ; n > 1; n-- {
		value = calcMod(value * n)
	}
	return value
}

func combinationMod(n, k int) int {
	factN := factMod(n)
	factK := factMod(k)
	factNK := factMod(n - k)
	factKR := powMod(factK, mod - 2)
	factNKR := powMod(factNK, mod - 2)
	return calcMod(factN * calcMod(factKR * factNKR))
}