#include <bits/stdc++.h>
using namespace std;
int main() {
  double a, b, c, s;
  cin >> a >> b >> c;
  s = (a * a * a) / (6 * sqrt(2)) + b * b * b * sqrt(2) / 6 +
      c * c * c * (5 + sqrt(5)) / 24;
  printf("%0.10f", s);
}
