#include <bits/stdc++.h>
using namespace std;

double l, t, c;
int main() {
  while (cin >> l >> t >> c && (l + t + c) >= 0.0) {
    double lp = (1 + t * c) * l;
    double theta_lo = 0.0;
    double theta_hi = M_PI;
    double theta_m = (theta_lo + theta_hi) / 2.0;
    double r = lp / theta_m;
    double try_l;
    if (abs(lp - l) < 1e-8) {
      cout << fixed << setprecision(3) << 0.000 << endl;
    } else {
      int n = 100;
      while (n--) {
        theta_m = (theta_lo + theta_hi) / 2.0;
        r = lp / theta_m;
        try_l = 2.0 * r * cos((M_PI - theta_m) / 2.0);
        if (try_l > l) {
          theta_lo = theta_m;
        } else {
          theta_hi = theta_m;
        }
      }
      double result = r - r * sin((M_PI - theta_lo) / 2.0);

      cout << fixed << setprecision(3) << result << endl;
    }
  }

  return 0;
}