InputBox: Cancel/X properties

This macro adds a comment to a cell and some text from an input box. I store the last value entered in the input box via the registry, it is recalled as the default input box value.

How do I capture the cancel property (Boolean, true or false?) so the ActiveCell.Value remains and comment is not added?

When a user selects Cancel/X the macro deletes the value in the cell and add's a comment. This overwrites existing data with "" (nothing).

The VBA help file wasn't very helpful, or, I did not know what to look for.

Sub AddComment()
'Special thanks to shg of excelforum.com

Dim x As String
Dim y As String

x = GetSetting("LastComment", "Variables", "x")
x = InputBox("Enter text", "Enter Comment", x)
SaveSetting "LastComment", "Variables", "x", x

With ActiveCell
    If Not .Comment Is Nothing Then .Comment.Delete
        .AddComment.Text Text:="35:" & vbLf & _
                "Do not delete comment"
        .Value = x
End With
'If user selects "Cancel/X" cell value is deleted and comment added?
End Sub

Any hints, tips or examples are appreciated.