#include <bits/stdc++.h>
using namespace std;
int main() {
  const double PI = 3.14159265358979323846264338;
  double a, b, c;
  cin >> a >> b >> c;
  double sum = sqrt(2) / 12 * (pow(a, 3) + 2 * pow(b, 3));
  double temp = c * 0.5 / cos(0.3 * PI);
  double s = 2.5 * temp * temp * sin(0.4 * PI);
  double h = sqrt(c * c - temp * temp);
  double v = s * h / 3;
  sum += v;
  printf("%.12lf", sum);
}
