#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1);
int main() {
  double a, b, c;
  cin >> a >> b >> c;
  double ans = sqrt(2) * a * a * a / 12.0;
  ans += sqrt(2) * b * b * b / 6.0;
  double ang = (54.0 * pi) / 180.0;
  double p = c / (2.0 * cos(ang));
  double q = sqrt(p * p - c * c * 0.25);
  double area = c * q * 0.5 * 5;
  double h = sqrt(c * c - p * p);
  double vol = (1.0 / 3.0) * area * h;
  ans += vol;
  printf("%.15lf\n", ans);
  return 0;
}
