#include<bits/stdc++.h> using namespace std; int main(){ double x1,x2,y1,y2; cin>>x1>>y1>>x2>>y2; printf("%0.3lf",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))); return 0; }

#include**<bits/stdc++.h>** using namespace std; int main(){** ** double x1,x2,y1,y2;** ** cin>>x1>>y1>>x2>>y2;** ** printf("%0.3lf",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));** ** return 0;** ** }

#include<bits/stdc++.h>
using namespace std;
int main(){
double x1,x2,y1,y2; 
cin>>x1>>y1>>x2>>y2; 
printf("%0.3lf",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))); 
return 0; }