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

int main() {
  double r, h, d; cin >> r >> h >> d;
  double sq = sqrt(4 * r * r - d * d);
  cout << setprecision(20)
       << ((log(abs(h * sq - 2 * h * r) / (2 * h * r))
            + 6 * log((sq + 2 * r) / h * (4 * r))
            - log(sq / (2 * r) + 1)
            - 6 * log(4 * d * r / h)) * d * d * d * h
           - 16 * h * d * r * sq
           + 32 * h * acos(d / (2 * r)) * r * r * r) / (48 * r) << '\n';
  return 0;
}