#include<iostream>
using namespace std;
int bx,by,cx,cy,ans=0,a[25][25];
void dfs(int x,int y){
	if(a[y][x]||x>bx||y>by)
		return;
	if(x==bx&&y==by){
		ans++;
	}
	if(x<bx)dfs(x+1,y);
	if(y<by)dfs(x,y+1);
}
int main(){
	cin>>by>>bx>>cy>>cx;
	a[cy][cx]=1,a[cy-2][cx-1]=1,a[cy-2][cx+1]=1,a[cy-1][cx+2]=1,a[cy+1][cx+2]=1,a[cy+2][cx+1]=1,a[cy+2][cx-1]=1,a[cy+1][cx-2]=1,a[cy-1][cx-2]=1;
	dfs(0,0);
	cout<<ans<<endl;
	return 0;
}