#include <bits/stdc++.h>
int main() {
  double x1, x2, x3;
  scanf("%lf%lf%lf", &x1, &x2, &x3);
  double ans = sqrt(2) / 12 * x1 * x1 * x1 + x2 * x2 * x2 / 3 / sqrt(2) +
               (5 + sqrt(5)) / 24 * x3 * x3 * x3;
  printf("%.10f", ans);
}
