#include <bits/stdc++.h>
using namespace std;
int main() {
#pragma warning(disable : 4996)
  double l3, l4, l5, v;
  const double PI = 3.141592653589;
  cin >> l3 >> l4 >> l5;
  v = l3 * l3 * l3 * sqrt(2.0) / 12 + l4 * l4 * l4 / sqrt(2.0) / 3 +
      5 * l5 * l5 * l5 / 24 / (5 - 2 * sqrt(5.0)) * sqrt(14 - 6 * sqrt(5.0));
  cout.precision(10);
  cout << v;
  return 0;
}
