#include <bits/stdc++.h>
using namespace std;
int main() {
  double a, b, c;
  scanf("%lf%lf%lf", &a, &b, &c);
  double res = pow(a, 3) * sqrt(2) / 12.0;
  res += pow(b, 3) * sqrt(2) / 6.0;
  double S = 1 / 4.0 * sqrt(25 + 10 * sqrt(5)) * c * c;
  double r = S * 2 / (5 * sin(2 * 3.141592654 / 5.0));
  double h = sqrt(c * c - r);
  res += S * h / 3.0;
  printf("%.12lf", res);
  return 0;
}
