#include <bits/stdc++.h>
using namespace std;
int main(void) {
  double a, b, c, t;
  cin >> a >> b >> c;
  t = sqrt(2.0) * a * a * a / 12;
  t += sqrt(2.0) * b * b * b / 6;
  t += 5.0 * c * c * c / 24.0 / tan(36.0 / 180.0 * 3.1415926535897) *
       sqrt(3.0 - 1 / (tan(36.0 / 180.0 * 3.1415926535897) *
                       tan(36.0 / 180.0 * 3.1415926535897)));
  printf("%.12f", t);
  return 0;
}
