#include <bits/stdc++.h>
using namespace std;
int main() {
  double l3, l4, l5;
  cin >> l3 >> l4 >> l5;
  double ans3 = sqrt(2) / 12.0 * l3 * l3 * l3;
  double h4 = sqrt(l4 * l4 / 2.0);
  double ans4 = l4 * l4 * h4 / 3.0;
  double l =
      l5 * sin(3.0 * 3.141592653589 / 10.0) / sin(2.0 * 3.141592653589 / 5.0);
  double h5 = sqrt(l5 * l5 - l * l);
  double di = 5.0 / 2.0 * l * l5 * sin(3.0 * 3.141592653589 / 10.0);
  double ans5 = di * h5 / 3.0;
  cout << fixed << setprecision(12) << ans3 + ans4 + ans5 << endl;
  return 0;
}
