#include <stdio.h>
#include <math.h>
int main()
{
    double a,b,c,d,e,f;
    scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f);
    printf("%.2lf",
        sqrt(//海伦公式
                (//p
                    sqrt(//(a,b)到(c,d)
                            (   
                                (a-c)*(a-c)+(b-d)*(b-d)
                            )
                        )+
                    sqrt(//(a,b)到(e,f)
                            (
                                (a-e)*(a-e)+(b-f)*(b-f)
                            )
                        )+
                    sqrt(//(c,d)到(e,f)
                            (
                                (c-e)*(c-e)+(d-f)*(d-f)
                            )
                        )
                )/2*
                (//p-a
                    (
                        sqrt(//同上
                                (
                                    (a-c)*(a-c)+(b-d)*(b-d)
                                )
                            )+
                        sqrt(
                                (
                                    (a-e)*(a-e)+(b-f)*(b-f)
                                )
                            )+
                        sqrt(
                                (
                                    (c-e)*(c-e)+(d-f)*(d-f)
                                )
                            )
                    )/2-a
                )*
                (//p-b
                    (
                        sqrt(
                                (
                                    (a-c)*(a-c)+(b-d)*(b-d)
                                )
                            )+
                        sqrt(
                                (
                                    (a-e)*(a-e)+(b-f)*(b-f)
                                )
                            )+
                        sqrt(
                                (
                                    (c-e)*(c-e)+(d-f)*(d-f)
                                )
                            )
                    )/2-b
                )*
                (//p-c
                    (
                        sqrt(
                                (
                                    (a-c)*(a-c)+(b-d)*(b-d)
                                )
                            )+
                        sqrt(
                                (
                                    (a-e)*(a-e)+(b-f)*(b-f)
                                )
                            )+
                        sqrt(
                                (
                                    (c-e)*(c-e)+(d-f)*(d-f)
                                )
                            )
                    )/2-c
                )
            )
    );
    return 0;
}