mov edx, [esp+8]
  cmp edx, 0
  ja @f
  mov eax, 0
  ret

  @@:
  cmp edx, 2
  ja @f

  mov eax, 1
  ret

  @@:
  push ebx
  mov ebx, 1
  mov ecx, 1


  @@:
      lea eax, [ebx+ecx]
      cmp edx, 3
      jbe @f

      mov ebx, ecx
      mov ecx, eax
      dec edx
      jmp @b

  @@:
  pop ebx
  ret