#include <bits/stdc++.h>
int main() {
  int x, y, z;
  double a, b, c, pi = 2 * acos(0.00), angle, m, n;
  scanf("%d%d%d", &x, &y, &z);
  angle = tan((3 * pi) / 10);
  m = sqrt(3 - angle * angle);
  a = x * x * x / (6 * sqrt(2));
  b = y * y * y / (3 * sqrt(2));
  c = (z * z * z) * angle * m;
  n = (c * 5 / 24) + a + b;
  printf("%.12lf\n", n);
  return 0;
}
