package main

import (
    "fmt"
)

func main() {
    var a, b, c, d int 
    fmt.Scanf("%d %d", &a, &b)
    fmt.Scanf("%d %d", &c, &d)

    ans := a * d - b * c

	fmt.Printf("%d\n", ans)
	
}

package main

import (
	"fmt"
	"strings"
)

func main() {
    var N, X int
    fmt.Scanf("%d %d", &N, &X)
	
	var S string
    fmt.Scanf("%s", &S)

	result := strings.Split(S, "")

	for i:=0; i<N; i++{
		if result[i] == "o"{
			X += 1
		} else if X > 0{
			X -= 1
		}
	}

	fmt.Printf("%d\n", X)
	
}

package main

import (
	"fmt"
	"math"
)

func main() {
    var r1, r2, c1, c2 int
    fmt.Scanf("%d %d", &r1, &c1)
    fmt.Scanf("%d %d", &r2, &c2)
	
	var ans int 

	if (r1 == r2) && (c1 == c2){
		ans = 0		
	} else if (r1+c1 == r2+c2) || (r1-c1 == r2-c2) || math.Abs(float64(r1-r2)) + math.Abs(float64(c1-c2)) <=3{
		ans = 1
  	} else if ((r2 - r1 + c2 - c1) % 2 == 0) || (math.Abs(float64(r2 - r1 - c2 + c1)) <= 3) || (math.Abs(float64(r2 - r1 + c2 - c1)) <= 3){
		ans = 2
	} else {
		ans = 3
	}

	fmt.Printf("%d\n", ans)
	
}

package main

import (
	"fmt"
)

var dp [101][101][101]float64

//Recursive function that returns the expected value of the move
func f(a int, b int, c int) float64{
	//If you have already calculated
	if dp[a][b][c] != 0{
		return dp[a][b][c]
	}

	//If you have reached the goal, the expected value of movement is 0
	if (a == 100) || (b == 100) || (c == 100) {
		return 0
	} 

	var ans float64 = 0
	
	ans += (f(a+1, b, c) + 1) * float64(a) / float64(a + b + c)
	ans += (f(a, b+1, c) + 1) * float64(b) / float64(a + b + c)
	ans += (f(a, b, c+1) + 1) * float64(c) / float64(a + b + c)

	dp[a][b][c] = ans
	return ans

}

func main() {

	var A, B, C int
    fmt.Scanf("%d %d %d", &A, &B, &C)

	fmt.Printf("%f\n", f(A, B, C))

}

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