#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
long double R,H,D,A;
long double f(long double x)
{
	long double sq=sqrt(4-(A/x)*(A/x));
	return A*A*log(sqrt(4*x*x-A*A)+2*x)/8-x*x/3*sq-A*A/24*log(x*(sq+2))+2*x*x*x*acos(A/(2*x))/(3*A);
}
main()
{
	cin>>R>>H>>D;
	A=D*H/R;
	cout<<fixed<<setprecision(16)<<D*D/A*(f(H)+A*A/24*log(A)-A*A*log(A)/8)<<endl;
}