#include <bits/stdc++.h>
using namespace std;
int main() {
  double L3, L4, L5;
  cin >> L3 >> L4 >> L5;
  double m_pi = 4.0 * atan(1.0);
  double v3 = L3 * L3 * L3 / 3 / 2 / sqrt(2);
  double v4 = L4 * L4 * L4 / 3 / sqrt(2);
  double v5 = L5 * L5 * L5 / 24 * (5 + sqrt(5));
  double result = v3 + v4 + v5;
  cout << setprecision(15) << result << endl;
  return 0;
}
