#include<bits/stdc++.h>
using namespace std;
int main(){
	int x1,y1;
	cin>>x1>>y1;
	int x2,y2;
	cin>>x2>>y2;
	int dm = abs(x1-x2)+abs(y1-y2);
	double de = sqrt(pow(x1-x2,2)+pow(y1-y2,2));
	cout<<fixed<<setprecision(6)<<abs(dm-de);
	return 0;
}