#include<bits/stdc++.h>
using namespace std;
int a[25][25];
int main(){
	int bi,bj,mi,mj;
	cin>>bi>>bj>>mi>>mj;
	a[0][0]=1;
	a[mi][mj]=-1;
	a[mi-1][mj-2]=-1;
	a[mi-2][mj-1]=-1;
	a[mi+1][mj-2]=-1;
	a[mi+2][mj-1]=-1;
	a[mi-2][mj+1]=-1;
	a[mi-1][mj+2]=-1;
	a[mi+1][mj+2]=-1;
	a[mi+2][mj+1]=-1;
	for(int i=0;i<=bi;i++){
		for(int j=0;j<=bj;j++){
			if(a[i][j]==-1){
				a[i][j]=0;
				continue;
			}	
			if(i==0&&j==0){
				continue;
			}
			if(i==0){
				a[i][j]=a[i][j-1];
				continue;
			}
			else if(j==0){
				a[i][j]=a[i-1][j];
				continue;
			}
			else{
				a[i][j]=a[i-1][j]+a[i][j-1];
				continue;
			}
		}
	}
	cout<<a[bi][bj];
	return 0;
}