#include <bits/stdc++.h>
using namespace std;
int main() {
  double a, b, c;
  cin >> a >> b >> c;
  double Rh = 1 / 10.0 * sqrt(50 + 10 * sqrt(5)) * c;
  double hh = sqrt(c * c - Rh * Rh);
  double Ah = 1 / 4.0 * sqrt(25 + 10 * sqrt(5)) * c * c;
  double Rc = b / sqrt(2);
  double hc = sqrt(b * b - Rc * Rc);
  double Ac = b * b;
  double Rt = a / sqrt(3);
  double ht = sqrt(a * a - Rt * Rt);
  double At = a * a * sqrt(3) / 4;
  printf("%.09f\n", (Ah * hh + Ac * hc + At * ht) / 3);
}
