#include<bits/stdc++.h>
using namespace std;

int main()
{
	int s[40][40];
	int a,b,c,d;
	
	cin>>a>>b>>c>>d;
	
	for(int i=0 ; i<=40 ; i++)
	{
		for(int j=0 ; j<=40 ; j++)
		{
			s[i][j] = 1;
		}
	}
	
	s[c-2][d+1] = s[c-1][d+2] = s[c+2][d+1] = s[c+1][d-2] = -1;
	s[c-2][d-1] = s[c-1][d-2] = s[c+2][d-1] = s[c+1][d-2] = s[c][d] = -1;
	
	for(int i=0 ; i<=a ; i++)
	{
		for(int j=1 ; j<=b ; j++)
		{
			if( s[i][j] == -1 && s[i+1][j-1] != -1) s[i+1][j] = s[i+1][j-1];
			else if( s[i+1][j-1] == -1 && s[i][j] != -1) s[i+1][j] = s[i][j];
			else if( s[i][j] == -1 && s[i+1][j-1] == -1) s[i+1][j] = 0;
			else if( s[i][j] != -1 && s[i+1][j-1] != -1) s[i+1][j] = s[i+1][j-1] + s[i][j];
		}
	}
	
	cout<<s[a][b]<<endl;
	return 0;
}