#include<stdio.h>
int a,b,c,d,ans;
void dfs(int x,int y)
{
	if(x>c||y>d||x<0||y<0)
	return;
	if(x==c&&y==d)
	{
		ans++;
		return;
	}
	if(!(((x==(a-2))&&(y==(b-1)))||((x==(a-1))&&(y==(b-2)))||((x==(a+1))&&(y==(b-2)))||((x==(a+2))&&(y==(b-1)))||((x==(a-2))&&(y==(b+1)))||((x==(a-1))&&(y==(b+2)))||((x==(a+2))&&(y==(b+1)))||((x==(a+1))&&(y==(b+2)))||(x==a&&y==b)))
	{
		dfs(x+1,y);
		dfs(x,y+1);
	}
}
int main()
{
	scanf("%d%d%d%d",&c,&d,&a,&b);
	dfs(0,0);
	printf("%d",ans);
	return 0;
}