#include <bits/stdc++.h>
using namespace std;

int main(){
	int xa,ya,xb,yb;
	cin>>xa>>ya>>xb>>yb;
	if(ya==yb){
		cout<<fixed<<setprecision(3)<<max(xa,xb)-min(xa,xb)<<endl;
		return 0;
	}
	if(xa==xb){
		cout<<fixed<<setprecision(3)<<max(ya,yb)-min(ya,yb)<<endl;
		return 0;
	}
	int xc=max(xa,xb),yc=max(ya,yb);
	cout<<fixed<<setprecision(3)<<sqrt((xc-min(xa,xb))*(xc-min(xa,xb))+(yc-min(ya,yb))*(yc-min(ya,yb)))<<endl;
	return 0;
}