求用VBA宏

Private Sub Workbook_Open()
        Dim str As String
        With Sheet1
              If Date < .Range("a1") Then
res:             str = InputBox("输入密码：", "Passwd")
                    If StrPtr(str) = 0 Then
                            Application.Quit
                    ElseIf str = .Range("a2") Then
                            MsgBox "welcome!"
                    ElseIf str <> .Range("a2") Then
                            MsgBox "密码错误"
                            GoTo res:
                    End If
              Else
                    MsgBox "系统日期>=a1"
                    Application.Quit
              End If
        End With
End Sub