#include <bits/stdc++.h>
using namespace std;
int main() {
  double a, b, c;
  cin >> c >> b >> a;
  double s = 0;
  s += c * c * c * (sqrt(2.0)) / 12;
  s += (b * b * b * sqrt(2)) / 6;
  s += (5 * a * a * a * tan(0.3 * 3.14159265358979323846) *
        tan(0.3 * 3.14159265358979323846) *
        sqrt(3 * (tan(0.2 * 3.14159265358979323846)) *
                 (tan(0.2 * 3.14159265358979323846)) -
             1)) /
       (24);
  cout << setprecision(15) << s;
  return 0;
}
