#include<stdio.h>
int a[100][100],counts;
int game(int,int,int,int);
int game(int x,int y,int zx,int zy)
{
	if(x==zx&&y==zy)
	{
		counts++;
		return 0;
	}
	if(x>=0&&x<zx&&a[x+1][y]!=1)
	{
		game(x+1,y,zx,zy);
	}
	if(y>=0&&y<zy&&a[x][y+1]!=1)
	{
		game(x,y+1,zx,zy);
	}
}
int main()
{
	int mx,my,x,y,zx,zy;
	scanf("%d%d%d%d",&zx,&zy,&mx,&my);
	a[my+2][mx+1]=a[my-2][mx+1]=a[my+2][mx-1]=a[my-2][mx-1]=a[my+1][mx+2]=a[my+1][mx-2]=a[my-1][mx+2]=a[my-1][mx-2]=a[my][mx]=1;
	game(0,0,zx,zy);
	printf("%d",counts);
	return 0;
}