#include <bits/stdc++.h>
const double PI = acos(-1.0);
double volume(double l, int n);
int main() {
  double l1, l2, l3;
  while (scanf("%lf%lf%lf", &l1, &l2, &l3) == 3) {
    printf("%.12f\n", volume(l1, 3) + volume(l2, 4) + volume(l3, 5));
  }
  return 0;
}
double volume(double l, int n) {
  double r = l / 2 / sin(PI / n);
  double h = sqrt(l * l - r * r);
  return n * r * r / 2 * sin(2 * PI / n) * h / 3;
}
