#include <bits/stdc++.h>
using namespace std;
const double _PI = 3.141592653589793;
double n, m, k, ans = 0;
signed main() {
  scanf("%lf %lf %lf", &n, &m, &k);
  ans += ((n * n * sqrt(3)) / 4) * (sqrt(n * n * 2 / 3)) / 3;
  ans += (m * m) / 3 * (sqrt(m * m / 2));
  double S = (k * k * 5) / (4 * tan(_PI / 5)), r = S / (2.5 * k);
  ans += S * sqrt(3 * k * k / 4 - r * r) / 3;
  printf("%0.12lf", ans);
}
