#include<iostream>
using namespace std;

int horsex,horsey,bx,by,cnt;
int a[22][22],visit[22][22];
int dx[4]={0,1};
int dy[4]={1,0};

bool horse(int x,int y){
	
	if(horsex==x&&horsey==y) return 0;
	if(horsex==x+1&&horsey==y+2) return 0;
	if(horsex==x+1&&horsey==y-2) return 0;
	if(horsex==x-1&&horsey==y+2) return 0;
	if(horsex==x-1&&horsey==y-2) return 0;
	if(horsex==x+2&&horsey==y-1) return 0;
	if(horsex==x+2&&horsey==y+1) return 0;
	if(horsex==x-2&&horsey==y-1) return 0;
	if(horsex==x-2&&horsey==y+1) return 0;
	
	return 1;
}

void dfs(int x,int y){
	if(x==bx&&y==by){
		cnt++;
		return;
	}
	
	for(int i=0;i<2;i++){
		if(a[dx[i]+x][dy[i]+y]&&!visit[dx[i]+x][dy[i]+y]){
			visit[dx[i]+x][dy[i]+y]=1;
			dfs(dx[i]+x,dy[i]+y);
			visit[dx[i]+x][dy[i]+y]=0;
		}
	}
	
	
}

int main(){
	
	cin>>bx>>by>>horsex>>horsey;
	
	for(int i=0;i<bx+1;i++){	//能走的标1
		for(int j=0;j<by+1;j++){
			a[i][j]=horse(i,j);
		}
	}
	
	dfs(0,0);

	cout<<cnt;
	
	return 0;
}
//求求了