#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int main(){
  double x1,x2,y1,y2,ans;
  cin>>x1>>y1>>x2>>y2;
  ans=sqrt(pow(x1-x2,2)+pow(y1-y2,2));
  cout<<fixed<<ans<<endl;
}

