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

int main() {
    int x1,x2,y1,y2;
    cin>>x1>>y1;
    cin>>x2>>y2;
    double a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
    double b=fabs(x1-x2)+fabs(y1-y2);
    cout<<fixed<<setprecision(18)<<fabs(b-a);
}
// 64 位输出请用 printf("%lld")

fabs取绝对值