#include <queue>#include <stack>#include <math.h>#include <stdio.h>#include <stdlib.h>#include <iostream>#include <limits.h>#include <string.h>#include <algorithm>using namespace std;const double pi = acos(-1.0);const double eps = 1e-12;bool dy(double x,double y){return x > y + eps;}// x > y bool xy(double x,double y){return x < y - eps;}// x < y bool dyd(double x,double y){ return x > y - eps;}// x >= y bool xyd(double x,double y){return x < y + eps;} // x <= y bool dd(double x,double y) {return fabs( x - y ) < eps;} // x == ydouble r,a;double n,c,l,L;void bsearch(){double beg = 0.0,end = pi;while( xy(beg,end) ){double mid = (beg+end)/2;a = mid;r = L/mid;if( dy(2*L*sin(a/2),l*mid) )beg = mid;elseend = mid;}}int main(){while( ~scanf("%lf%lf%lf",&l,&n,&c) ){if( l == n && l == c && c == -1 )break;if( dd(l,0.0) || dd(n,0.0) || dd(c,0.0) ){printf("0.000n");continue;}L = (1+n*c)*l;bsearch();double ans = L/a - (L*cos(a/2)/a);printf("%.3lfn",ans);}return 0;}
