#include <bits/stdc++.h>
using namespace std;
double pi = acos(-1);
int main() {
  double t, s, f, v1, v2, v3;
  cin >> t >> s >> f;
  v1 = sqrt(2) * t * t * t / 12.0;
  v2 = sqrt(2) * s * s * s / 6.0;
  double d = tan(3.0 / 10.0 * pi) * f / 2.0;
  double l = sqrt(d * d + f * f / 4.0);
  double h = sqrt(f * f - l * l);
  v3 = d * f / 2.0 * 5.0 * h / 3.0;
  printf("%.12lf", v1 + v2 + v3);
  return 0;
}
