#include <bits/stdc++.h>
using namespace std;
struct skill {
  int level;
  bool operator<(const skill &that) const {
    return level % 10 > that.level % 10;
  }
};
long long p(int n, int e) {
  long long res = 1;
  for (int i = 0; i < e; i++) res *= n;
  return res;
}
int main() {
  double pi = 3.14159265358979323846;
  int l3, l4, l5;
  cin >> l3 >> l4 >> l5;
  double v3 = l3 * l3 * l3 * sqrt(2.0) * 0.25;
  double v4 = l4 * l4 * l4 * sqrt(2.0) * 0.5;
  double b = l5 / (2 * sin(pi / 5));
  double h = sqrt(l5 * l5 - b * b);
  double v5 = 2.5 * b * b * h * sin(2 * pi / 5);
  double res = v3 + v4 + v5;
  res /= 3;
  printf("%.15lf\n", res);
  return 0;
}
