#include <math.h>

struct tetrahedron {
    double a,b,c,ea,eb,ec;
    double volume() const {
        double A=a*a, B=b*b, C=c*c, X=B+C-ea*ea, Y=A+C-eb*eb, Z=A+B-ec*ec;
        return sqrt(4*A*B*C-A*X*X-B*Y*Y-C*Z*Z+X*Y*Z)/12;
    }
};

#include <stdio.h>

int main(int argc,char** argv) {
    tetrahedron t;
    t.a=1;  t.b=1;  t.c=1;
    t.ea=1; t.eb=1; t.ec=1;
    double V=t.volume(), V0=sqrt(2)/12;
    printf("V=%.5f (%.5f)\n",V,V0);
    return 0;
}