using namespace std;
long long p1=0,p2=0,e1,e2,h1,h2,mp[21][21],num=0;
void nxt(){
	if(mp[p1][p2]==2)
		num++;
	else if(p1+1<=e1&&mp[p1+1][p2]!=3){
		p1++;
		nxt();
		p1--;
	}
	else if(p2+1<=e2&&mp[p1][p2+1]!=3){
		p2++;
		nxt();
		p2--;
	}
}
int main(){
	cin>>e1>>e2>>h1>>h2;
	mp[e1][e2]=2;
	mp[h1][h2]=3;
	mp[h1+2][h2+1]=3;mp[h1+1][h2+2]=3;
	mp[h1+2][h2-1]=3;mp[h1-1][h2+2]=3;
	mp[h1-2][h2+1]=3;mp[h1+1][h2-2]=3;
	mp[h1-2][h2-1]=3;mp[h1-1][h2-2]=3;
	if(p1+1<=e1&&mp[p1+1][p2]!=3){
		p1++;
		nxt();
		p1--;
	}
	else if(p2+1<=e2&&mp[p1][p2+1]!=3){
		p2++;
		nxt();
		p2--;
	}
	cout<<num;
	return 0;
}