#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main(){
double x1,x2,y1,y2,distance,d;
cin>>x1>>y1;
cin>>x2>>y2;
d=((x2-x1)*(x2-x1))+((y2-y1)*(y2-y1));
distance = sqrt(d);
cout<<setiosflags(ios::fixed)<<setprecision(4)<<distance<<endl;
return 0;
}