#include <bits/stdc++.h>
using namespace std;
int main() {
  const double PI = 2 * asin(1.0);
  int l1, l2, l3;
  double v1, v2, v3;
  cin >> l1 >> l2 >> l3;
  v1 = (sqrt(2) * pow(l1, 3)) / 12;
  v2 = pow(l2, 3) / (3 * sqrt(2));
  v3 = (5 * (pow(l3, 3)) / (12 * tan(PI / 5))) *
       (sqrt(1 - (1 / (4 * pow(sin(PI / 5), 2)))));
  cout << setprecision(14) << v1 + v2 + v3;
  return 0;
}
