Before save, prompt message box with yes/no/cancel. Yes calls Macro, No continues to save, Cancel exits sub

I already have a successful "custom save" macro to save-as with a date stamp. I just want to have a message box ask to run it when someone tries to manually save. I essentially need "yes" to run the macro, "no" to save normally, and "cancel" to exit sub.

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)

Dim answer As VbMsgBoxResult
answer = msgbox("Would you rather Save-As copy with date stamp?", vbYesNoCancel + vbQuestion + vbDefaultButton1, "You are overwriting the document!")

If answer = vbYes Then
        Call filesave
    ElseIf answer = vbNo Then
        ActiveWorkbook.Save
    Else
        Exit Sub

End If

End Sub