#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>

using namespace std;

#define NMAX 1000

double calc(double x1,double y1,double x2,double y2){
	return abs(sqrt(pow(x1-x2,2)+pow(y1-y2,2)));
}

int main(){

	double xa,ya,xb,yb;
	double min_n,min_i;

	cin>>xa>>ya;
	cin>>xb>>yb;

	if(ya<yb){
		swap(ya,yb);
		swap(xa,xb);
	}

	min_n=calc(0,ya,xa,ya)+calc(0,ya,xb,yb);
	min_i=ya;

	for(double i=ya+1;i>=yb-1;i--){
		double c=calc(0,i,xa,ya)+calc(0,i,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=i;
		}
	}

	double t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.1;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}

	t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.01;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}

	t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.001;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}

	t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.0001;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}

	t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.00001;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}

	t=min_i;
	for(int i=-10;i<=10;i++){
		double ii=t+i*0.000001;
		double c=calc(0,ii,xa,ya)+calc(0,ii,xb,yb);
		if(c<min_n){
			min_n=c;
			min_i=ii;
		}
	}
	printf("%.7f\n",min_i);
}