int main()
{
    double a,b,c,d,s,e,S;
    scanf("%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e);
    s=(a+b+c+d)/2;
    if((s-a)*(s-b)*(s-c)*(s-d)>0)
    {S=sqrt((s-a)*(s-b)*(s-c)*(s-d)-a*b*c*d*cos(e/360*3.1415926)*cos(e/360*3.1415926));
    printf("%.4lf",S);}
    else
    printf("Invalid input");
    return 0;
}