#include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 const double eps=1e-;

 double n,c,l;

 int main()

 {

     while(scanf("%lf%lf%lf",&l,&n,&c)&&l!=-&&n!=-&&c!=-){

         double s=(+n*c)*l;

         double low=,high=0.5*l,mid;

         while(high-low>eps)

         {

             mid=(high+low)/;

             double r=(*mid*mid+l*l)/(*mid);

             double ss=*r*asin(l/(*r));

             if(ss<s)

                 low=mid;

             else

                 high=mid;

         }

         printf("%.3lf\n",mid);

     }

     return ;

 }