*answer = 42
book->title = Bumi Manusia
shelf[4].id = B4005, year 2004
  grow: capacity 1, copied 0
  grow: capacity 2, copied 1
  grow: capacity 4, copied 2
  grow: capacity 8, copied 4
  grow: capacity 16, copied 8
  grow: capacity 32, copied 16
size 17, capacity 32, last 289, total copies 31 (< 2 * 17 = 34)
