> #include<stdio.h>
> #include<string.h>
> #include<math.h>
> double  INF;
> 
> double  ll;
> double  find(double len)
> {
>     double r = INF, l = 0;
>     double  mid, tmp;
>     int  i;
>     //while(fabs(r-l) > 1e-12)
>     for(i = 0; i < 100; i++)
>     {
>         mid = (l+r)/2;
>         tmp = 2*mid*asin(len/2/mid);
> 		//printf("%lf\n", tmp);
>         if(fabs(tmp-ll) < 1e-12) return  mid;
>         else  if(tmp < ll)
>             r = mid;
>         else  l = mid;
>     }
> 	return 0;
> }
> 
> 
> int  main()
> {
>     double l, t, c;
>     double  tmp;
> 	INF = 400000000;
> 	INF *= INF;
>     while(scanf("%lf %lf %lf", &l, &t, &c) != EOF && fabs(l+1) > 1e-12)
>     {
>         if(fabs(l) < 1e-12){ printf("0.000\n"); continue; }
>         ll = (1+t*c)*l;
> 		tmp = find(l);
>         printf("%.3lf\n", tmp-sqrt(tmp*tmp-l*l/4));
>     }
>     return 0;
> }
 
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