#include <bits/stdc++.h>
using namespace std;
int main() {
  double l1, l2, l3;
  double v1, v2, v3;
  scanf("%lf%lf%lf", &l1, &l2, &l3);
  v1 = (sqrt(2) * (l1 * l1 * l1)) / 12;
  v2 = (sqrt(2) * (l2 * l2 * l2)) / 6;
  v3 = ((5 + sqrt(5)) * (l3 * l3 * l3)) / 24;
  printf("%.10f\n", v1 + v2 + v3);
  return 0;
}
