#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int main(){
float x1,x2,y1,y2,d;
cout<<"dose tis suntetagmenes ton 2 shmion";
cin>>x1>>y1>>x2>>y2;
d=sqrt(pow(x2-x1,2)+pow(y2-y1,2));
cout<<fixed<<setprecision(2)<<d;
return 0;
}