#include<cstdio>
#include<cstdlib>

int n,m;
int p1,p2;
int pomi;

void read();
int cmmdc(int x, int y);
void write();

int main() {
	read();
	write();
}

void read() {
	freopen("mins.in","r",stdin);
	scanf("%d%d%d%d",&n,&m,&p1,&p2);
}

int cmmdc(int x, int y) {
	if (y==0) return x;
	return cmmdc(y,x%y);
}

void write() {
	freopen("mins.out","w",stdout);
	int i,j,c;
	for (i=1;i<n;++i) {
		for (j=1;j<m;++j) {
			int x,y;
			x=abs(p1-i);
			y=abs(p2-j);
			
			if (x==0 && y==1) c=1;
			else if (y==0 && x==1) c=1;
			else if (x==0 || y==0) c=0;
			else c=cmmdc(x,y);
			
			if (c==1) ++pomi;
		}
	}
	printf("%d",pomi);
}