#include<stdio.h>
long long int k[25][25];
int main()
{
	int fun(int x,int y);
	int a,b,c,d,i,j;
	scanf("%d%d%d%d",&a,&b,&c,&d);
	for(i=0;i<=21;i++){
		for(i=0;i<=21;i++){
			k[i][j]=0;
		}
	}
	k[c-1][d+2]=-1;
	k[c-1][d-2]=-1;	
	k[c-2][d+1]=-1;
	k[c-2][d-1]=-1;	
	k[c+1][d+2]=-1;
	k[c+1][d-2]=-1;	
	k[c+2][d-1]=-1;
	k[c+2][d+1]=-1;
	k[c][d]=-1;
	printf("%lld",fun(a,b));
}
fun(int x,int y){
	if(k[x][y]==-1)
	return 0;
	if(x==0||y==0)
	return 1;
	if(k[x][y]==0){
		k[x][y]=fun(x-1,y)+fun(y,x-1);
	}
	return k[x][y];
}//8 6 0 4