/*
二分 + 几何
弧长L, 圆半径R, 弧度 q, L=R*q;
二分: 弧度(0~PI) 或者 高度(L/2~L)
*/
#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
const double PI = acos(-1.0);
double L, L1, T, C, R, Q;
int main(){
while(scanf("%lf%lf%lf", &L, &T, &C) && (L!=-1 || T!=-1 || C!=-1)){
L1 = (1+T*C)*L;
double ld=0.0, rd=PI, tmp;
Q = (ld+rd)/2;
R = L/2/sin(Q);
while(fabs(tmp = R*2*Q-L1)>1e-8){
if(tmp>0) rd=Q;
else ld=Q;
Q=(ld+rd)/2;
R = L/2/sin(Q);
}
printf("%.3lf\n", R-sqrt(R*R - (L/2)*(L/2)));
}
return 0;
}