#include<iostream>
using namespace std;
int xm,ym,zdx,zdy;
int cnt=0;
bool lan(int x,int y,int xm,int ym){
	if((x==xm+1&&y==ym+2)||(x==xm+2&&y==ym+1))return false;
	if((x==xm-1&&y==ym-2)||(x==xm-2&&y==ym-1))return false;
	if((x==xm-1&&y==ym+2)||(x==xm-2&&y==ym+1))return false;
	if((x==xm+1&&y==ym-2)||(x==xm+2&&y==ym-1))return false;
	return true;
}
void zu(int x,int y){
	if(x==xm&&y==ym)return;
	if(!lan(x,y,xm,ym))return;
	if(x>zdx)return;
	if(y>zdy)return;
	if(x==zdx&&y==zdy){
		cnt++;
		return;
	}
	zu(x+1,y);
	zu(x,y+1);
} 
int main(){
    cin>>zdx>>zdy>>xm>>ym;
    zu(0,0);
    cout<<cnt;



}