#include <bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c,d;
	cin>>a>>b>>c>>d; 
	int z[a+1][b+1]={0},j[a+1][b+1]={0};
	j[c][d]=-1;
	j[c-2][d-1]=-1;
	j[c-1][d-2]=-1;
	j[c+2][d+1]=-1;
	j[c+1][d+2]=-1;
	j[c-1][d+2]=-1;
	j[c+2][d-1]=-1;
	j[c+1][d-2]=-1;
	j[c-2][d+1]=-1;
	for(int i=0;i<=a;i++){
		if(j[i][b]!=-1)
		z[i][b]=1;
	}
	for(int e=0;e<=b;e++){
		if(j[a][e]!=-1)
		z[a][e]=1;
	}	
	for(int i=0;i<=a;i++){
	for(int e=0;e<=b;e++){
		if(j[i][e]!=-1){
			if(j[i-1][e]>=0)
			z[i][e]+=j[i-1][e]; 
			if(j[i][e-1]>=0)
			z[i][e]+=j[i][e-1]; 
		}
		else continue;
	}
}
cout<<z[i][e];
 	return 0;
}