#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1);
const double N = 1e-9;
int main() {
  int a, b, c;
  cin >> a >> b >> c;
  double s1, s2, s3 = sqrt(c * c / (2.0 - 2.0 * cos(72.0 * PI / 180.0))),
                 s = sqrt(s3 * s3 - c * c / 4.0);
  s3 = sqrt(c * c - s3 * s3);
  s = sqrt(3.0) * a * a * sqrt(a * a - sqrt(3) * a / 3.0 * sqrt(3) * a / 3.0) /
          12.0 +
      b * b * sqrt(b * b - sqrt(2) * b / 2.0 * sqrt(2) * b / 2.0) / 3.0 +
      s * c * s3 * 5.0 / 6.0;
  cout << fixed << setprecision(15) << s;
  return 0;
}
