#include <bits/stdc++.h>
using namespace std;
const double pi = 3.1415926535987;
double la, lb, lc;
int main() {
  scanf("%lf%lf%lf", &la, &lb, &lc);
  double Va, Vb, Vc;
  Va = (la * la * la * sqrt(2)) / 12;
  Vb = (lb * lb * lb * sqrt(2)) / 6;
  double A = pi * 3.0 / 10.0;
  Vc = lc / 2 * tan(A) * lc / 2 *
       sqrt((lc) * (lc)*3 / 4 - (lc / 2 * tan(A)) * (lc / 2 * tan(A)));
  Vc /= 3;
  Vc *= 5;
  printf("%.12lf", Va + Vb + Vc);
  return 0;
}
