> #include<cstring>
> #include<cstdio>
> #include<cmath>
> using namespace std;
> double l,n,c,l1,hi,lo,pi,mid,f;
> int main(void){
> 
>     while(true){
>         scanf("%lf %lf %lf",&l,&n,&c);
>         if(l<0 || n<0 ||c<0)break;
>         l1=l+n*c*l;
>         pi=3.1415926;mid=0;
>         hi=pi/2;lo=0;mid=(hi+lo)/2;
>         f=mid*l-sin(mid)*l1;
>         while (abs(f)>1e-12)
>         {         
>             if (f>0) hi=mid; else lo=mid;
>             mid=(hi+lo)/2;
>             f=mid*l-sin(mid)*l1;
>         }                
>         printf("%.3lf\n",l1/mid/2*(1-cos(mid)));
>     }
>     return 0;
> }