#include <bits/stdc++.h>
using namespace std;
double LaLa(double len, double num) {
  double a = len * len * len * num;
  double b = 12 * tan((acos(-1)) / num);
  double c =
      sqrt(1 - 1 / (4 * ((sin((acos(-1)) / num)) * (sin((acos(-1)) / num)))));
  return a * c / b;
}
int main() {
  double a, b, c, tot(0);
  scanf("%lf%lf%lf", &a, &b, &c);
  tot += LaLa(a, 3);
  tot += LaLa(b, 4);
  tot += LaLa(c, 5);
  printf("%.12lf", tot);
  return 0;
}
