#include <iostream>
#include "math.h"
using namespace std;


double V(double a,double b,double c,double m,double n,double l)
{
	return sqrt(4*a*a*b*b*c*c-a*a*(b*b+c*c-m*m)*(b*b+c*c-m*m)-b*b*(c*c+a*a-n*n)*(c*c+a*a-n*n)-c*c*(a*a+b*b-l*l)*(a*a+b*b-l*l)+(a*a+b*b-l*l)*(b*b+c*c-m*m)*(c*c+a*a-n*n));
}

double cos_x(int a,int b,int c)
{
	return double(a*a+b*b-c*c)/(2*a*b);
}
int main()
{
	int a,b,c,d,e,f;
	scanf("%d %d %d %d %d %d",&a,&b,&c,&d,&e,&f);
	printf("%.4f",V(a,b,c,d,e,f)/12);
	return 0;
}