#include <iostream>
#include <cstdlib>
#include <fstream>
#include <clocale>
#include <cmath>
#include <iomanip>
 
#define     iFILE       "input.txt"
#define     oFILE       "output.txt"
 
class Point {
    public:     double x;
    public:     double y;
};
 
int main(){setlocale(LC_ALL,"Rus");
    std::ifstream inp;inp.open(iFILE);
        while(!inp.is_open()){
            std::cout << "Файл не найден." << std::endl;
        system("pause");
        return 0;
        }
        Point A,B,C;
        inp >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y;
        std::ofstream ofs;ofs.open(oFILE);
            if( A.y<C.y && A.y>B.y  ||      
                A.y<B.y && A.y>C.y){        
                    double AB = sqrt(pow(C.x-A.x    ,2.0)+pow(C.y-A.y   ,2.0)); 
                    double AC = sqrt(pow(C.x-A.x    ,2.0)+pow(C.y-A.y   ,2.0)); 
                    double CB = sqrt(pow(C.x-B.x    ,2.0)+pow(C.y-B.y   ,2.0)); 
                    double p = (AB+AC+CB)/2;
                    double S = sqrt(p*(p-AB)*(p-AC)*(p-CB));
                    double Ah = (2*S)/CB;
            ofs << std::fixed << std::setprecision(4) << Ah;
            }
            else if(A.y==C.y && A.y>B.y || A.y==B.y && A.y>C.y){   
                        double Ah = sqrt(pow(C.x-A.x    ,2.0)+pow(C.y-A.y   ,2.0));
                ofs << std::fixed << std::setprecision(4) << Ah;
                }
            else 
                ofs << -1;
        ofs.close();
    inp.close();
return 0;
}