#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
double x1,y1,x2,y2,a,b,c;
cin>>x1>>y1>>x2>>y2;
a = abs(x1 - x2);
b = abs(y1 - y2);
c = a + b;
cout<<fixed<<setprecision(3)<<abs(c)<<endl;
return 0;
}