#include <cmath>

#include <iomanip>

#include <iostream>

using namespace std;


int main(){

double xx1,xx2,yy1,yy2;

double de,dm,derta;

cin>>xx1>>yy1>>xx2>>yy2;

Dm=sqrt((xx1-xx2)*(xx1-xx2)+(yy1-yy2)*(yy1-yy2));

De=fabs(xx1-xx2)+fabs(yy1-yy2);

derta=fabs(Dm-De);

cout<<fixed<<setprecision(6)<<derta<<endl;

return 0;
}