#include <bits/stdc++.h>
using namespace std;
int main(){
    double x1,y1,x2,y2;
    cin>>x1>>y1;
    cin>>x2>>y2; 
    double k1= pow(x1-x2,2);
    double k2= pow(y1-y2,2);
    
    double k3 = sqrt(k1+k2);
    cout<<fixed<<setprecision(3)<<k3;
	return 0;
	
	
}