#include<bits/stdc++.h>
using namespace std;
int main(){
	int a1,a2,b1,b2;
	cin>>a1>>a2>>b1>>b2;
	int q[23][23]={0};
	q[b1][b2]=-1;
	q[b1-2][b2-1]=-1;
	q[b1-2][b2+1]=-1;
	q[b1+2][b2-1]=-1;
	q[b1+2][b2+1]=-1;
	q[b1+1][b2+2]=-1;
	q[b1+1][b2+2]=-1;
	q[b1+1][b2+2]=-1;
	q[b1+1][b2+2]=-1;
	q[0][1]=1;
	for(int i=1;i<=a1;i++){
		for(int j=1;j<=a2;j++){
			if(q[i][j]==-1||q[i-1][j]==-1&&q[i][j-1]==-1)continue;
			if(q[i-1][j]==-1){
				q[i][j]=q[i][j-1];
				continue;
			}
			if(q[i][j-1]==-1){
				q[i][j]=q[i-1][j];
				continue;
			}
			q[i][j]=q[i-1][j]+q[i][j-1];
		}
	}
	cout<<q[a1][a2];
	return 0;
}