#include <iostream>
#include <cstdio>
#include <string.h>
#include <math.h>
#include <algorithm>

double Cos(double a,double b,double c)
{
    return (a*a+b*b-c*c)/(2.0*a*b);
}
int main()
{
    double a,b,c,d,e,f;
    while(scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f)!=EOF){
    double horna = Cos(c,e,a);
    double hornb = Cos(e,f,d);
    double hornc = Cos(f,c,b);
    double v = c*e*f*sqrt(1+2*horna*hornb*hornc-horna*horna-hornb*hornb-hornc*hornc)/6;
    printf("%.4lf\n",v);
    }
    return 0;
}