#include <cstdio>
#include <cmath>
const double ep = 1e-12;
const double pi = 3.1415926535897932324626;
int main()
{
	double l,l1,n,c,r,h;
	double x0,x1,k;
	scanf("%lf %lf %lf",&l,&n,&c);
	while(l >= 0 || n >= 0 || c >= 0)
	{
		l1 = l * (1.0 + n * c);
		k = l / l1;
		x0 = pi * 0.125;
		x1 = x0 - (sin(x0) - k * x0) / (cos(x0) - k);
		while(fabs(sin(x1) - k * x1) > ep && fabs(x1 - x0) > ep)
		{
			x0 = x1;
			x1 = x0 - (sin(x0) - k * x0) / (cos(x0) - k);
		}
		r = l1/2/x1;
		h = r * (1 - cos(x1));
		printf("%0.3lf\n",h);
		scanf("%lf %lf %lf",&l,&n,&c);
	}
	return 0;
}