=>WM:  1 [NIL] (A)
=>WM:  2 [NIL] (A)
23:  最初は１ 2
=>WM:  3 [最初は１] (COUNT 1)
<=WM:  2 [NIL] (A)
24:  要素があれば数える 1 3
=>WM:  4 [要素があれば数える] (COUNT 2)
<=WM:  3 [最初は１] (COUNT 1)
<=WM:  1 [NIL] (A)
25:  答えを返す 4
<=WM:  4 [要素があれば数える] (COUNT 2)