#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
//抄博友程序 读博友好分析 没掌握
int main()
{
while(1)
{
double l;
double n;
double c;
cin>>l>>n>>c;
if(l<0 && n<0 && c<0)
{
break;
}
double s=(1+n*c)*l;
double left=0;
double right=l/2.0;
//double jg;
double mid;//抄博友 背
while((right-left)>(1e-5))//抄博友程序
{
mid=(left+right)/2;
double r=(4.0*mid*mid+l*l)/(8.0*mid);
//cout<<mid<<" "<<r<<" "<<2*r*asin(l/(2*r))<<endl;
if(s>2*r*asin(l/(2*r)))
{
left=mid;
//jg=mid;
}else
{
right=mid;
}
}
cout<<fixed<<setprecision(3)<<mid<<endl;
}
return 0;
}
