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

int main() {
    int x1,y1,x2,y2;

    cin>>x1>>y1>>x2>>y2;
    int dx=x1-x2;
    int dy=y1-y2;
    double E,M;
    E=sqrt(dx*dx+dy*dy);
    M=fabs(dx)+fabs(dy);
    printf("%.10f",fabs(M-E));

}