#include <bits/stdc++.h>
using namespace std;
double PI;
double l[3], s[3], v[3];
int main() {
  PI = acos(-1.0);
  cin >> l[0] >> l[1] >> l[2];
  v[0] = sqrt(2) * l[0] * l[0] * l[0] / 12;
  v[1] = sqrt(2) * l[1] * l[1] * l[1] / 6;
  double x = sqrt(1 - 1 / (4 * sin(PI * 0.2) * sin(PI * 0.2)));
  v[2] = l[2] * l[2] * l[2] * 5 * x / tan(0.2 * PI) / 12;
  printf("%.12lf", v[0] + v[1] + v[2]);
  return 0;
}
