#include<bits/stdc++.h>
using namespace std;
long long  n[100][100],l[100][100],ax,ay,bx,by,cx,cy;
void f()
{
	n[cx][cy]=1;
	n[cx-1][cy-2]=1;
	n[cx-2][cy-1]=1;
	n[cx-2][cy+1]=1;
	n[cx-1][cy+2]=1;
	n[cx+1][cy-2]=1;
	n[cx+2][cy-1]=1;
	n[cx+2][cy+1]=1;
	n[cx+1][cy+2]=1;
}
int main()
{
	cin>>bx>>by>>cx>>cy;
	f();
	l[1][0]=1;
	for(int i=1;i<=bx+1;++i)
	   for(int j=1;j<=by+1;++j)
	   {
	   	l[i][j]=l[i-1][j]+l[i][j-1];
		if(n[i-1][j-1])l[i][j]=0;
	   }
	   cout<<l[bx+1][by+1];
	   return 0;
}