#include <bits/stdc++.h>
const double pi = acos(-1.0);
using namespace std;
double l1, l2, l3;
int main() {
  cin >> l1 >> l2 >> l3;
  double ans1 = sqrt(2.0) / 12.0 * l1 * l1 * l1;
  double ans2 = sqrt(2.0) / 6.0 * l2 * l2 * l2;
  double X = l3 / (2.0 * sin(pi / 5.0));
  double ans3 = X * X * sin(2.0 * pi / 5.0) * 5 * sqrt(l3 * l3 - X * X) / 6;
  printf("%.12lf\n", ans1 + ans2 + ans3);
}
