#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  double a, b, c;
  cin >> a >> b >> c;
  double ans = pow(a, 3) / (6 * sqrt(2)) + pow(b, 3) / (3 * sqrt(2)) +
               ((5 + sqrt(5)) / 24) * pow(c, 3);
  printf("%.17lf\n", ans);
}
