#include <bits/stdc++.h>
const int MAX_N = (int)1e5 + 123;
const double eps = 1e-6, pi = acos(-1);
const int inf = (int)1e9 + 123;
using namespace std;
long double a, b, c;
long double res;
int main() {
  cin >> a >> b >> c;
  res = b * b * b / sqrt(2.0) / 3.0;
  res += a * a * a * sqrt(2.0) / 12.0;
  double h = (1.0 / 10) * sqrt(50.0 + 10.0 * sqrt(5)) * c;
  h = h * h;
  h = c * c - h;
  h = sqrt(h);
  h *= tan(pi * 54.0 / 180.0) * c * c;
  h *= (5.0 / 12.0);
  res += h;
  cout << setprecision(20) << res << endl;
  return 0;
}
