#include<bits/stdc++.h>
using namespace std;
int main(){
	long long x1,y1,x,y;
	cin>>x1>>y1>>x>>y;
	long long a[x1+1][y1+1];
	for(int i = 0;i<=x1;i++)
	for(int j = 0;j<=y1;j++)a[i][j]=-1;
	a[x+2][y+1]=0;a[x+2][y-1]=0;
	a[x-2][y+1]=0;a[x-2][y-1]=0;
	a[x-1][y+2]=0;a[x-1][y-2]=0;
	a[x+1][y+2]=0;a[x+1][y-2]=0;
	a[x][y]=0;
	for(int i = 0;i<=x1;i++)
		for(int j = 0;j<=y1;j++){
			if(a[i][j]==0) continue;
			if(i==0||j==0) a[i][j]=1;
			else a[i][j]=a[i-1][j]+a[i][j-1];
		}
	cout<<a[x1][y1];
}