#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1.0);
const double EPS = 1e-12;
const double INF = 1e100;
int main() {
  double a, b, c;
  cin >> a >> b >> c;
  double v1, v2, v3;
  v1 = (double)((a * a * a * sqrt(2.0)) / 12.0);
  v2 = (double)((b * b * b) / (3.0 * sqrt(2)));
  double ang = (72.0 * PI) / 180.0;
  double x = (double)(c / sqrt(2.0 - 2.0 * cos(ang)));
  double ht = sqrt(x * x - (double)((c * c) / 4.0));
  double ab = (double)2.5 * c * ht;
  double htet = sqrt((double)(c * c) - x * x);
  v3 = (ab * htet) / 3.0;
  double ans = v1 + v2 + v3;
  printf("%.12lf\n", ans);
  return 0;
}
