#include<stdio.h>
using namespace std;
int a,b,c,d,f=0;
void dfs(int x,int y){
	if(x+1==c-1||x+1==c-2||x+1==c+1||x+1==c+2||x+1==c)
		if(y+1==d-1||y+1==d-2||y+1==d+1||y+1==d+2||y+1==d)
			return;
	if(a+1==x){
		f+=1;
		return;
	}
	if(b+1==y){
		f+=1;
		return;
	}
	if(x<a)
		dfs(x+1,y);
	if(y<b)
		dfs(x,y+1);
}
int main() {
	scanf("%d %d %d %d",&a,&b,&c,&d);
	dfs(1,1);
	printf("%d",f);
	return 0;
}