#include <bits/stdc++.h>
using namespace std;
const long double pi = 3.1415926535897932384;
__inline__ __attribute__((always_inline)) long double kkksc03(long double a,
                                                              long double b) {
  long double s;
  s = (a * a * a * b) / (12 * tan(pi / b)) *
      (sqrt(1 - (1 / (4 * sin(pi / b) * sin(pi / b)))));
  return s;
}
int main() {
  long double l3, l4, l5;
  cin >> l3 >> l4 >> l5;
  cout << fixed << setprecision(10)
       << kkksc03(l3, 3) + kkksc03(l4, 4) + kkksc03(l5, 5);
  return 0;
}
