1 /**
2 题解晚上写
3 **/
4 #include <iostream>
5 #include <math.h>
6 #include <algorithm>
7 #include <cstdio>
8 using namespace std;
9 const double esp = 1e-5;
10 int main()
11 {
12 double l,n,c;
13 while(cin>>l>>n>>c){
14 if(l<0&&n<0&&c<0)
15 break;
16 double ll;
17 ll = (1+n*c)*l;
18 double low,high;
19 low =0;
20 high= l/2;
21 double r,mid;
22 while(high-low>esp){
23 mid = (high+low)/2.0;
24 r = ((mid*mid*4)+(l*l))/(8*mid);
25 if(2*r*asin(l/(2*r))<ll)
26 low = mid;
27 else
28 high = mid;
29 }
30 printf("%.3lf\n",high);
31 }
32 return 0;
33 }
