#include<bits/stdc++.h>
using namespace std;
int xb,yb,xh,yh,ans;
void dp(int x,int y)
{
	if((x==xh&&y==yh)||(x==xh+2&&y==yh+1)||(x==xh+1&&y==yh+2)||(x==xh+1&&y==yh-2)||(x==xh+2&&y==yh-1)||(x==xh-2&&y==yh-1)||(x==xh-1&&y==yh-2)||(x==xh-1&&y==yh+2)||(x==xh-2&&y==yh+1)||x>xb||y>yb) return;
	if(x==xb&&y==yb)
	{
		ans++;
		return;
	}
	dp(x,y+1);
	dp(x+1,y);
}
int main()
{
	cin>>xb>>yb>>xh>>yh;
	dp(0,0);
	cout<<ans<<endl;
	return 0;
}