Zellentausch Makro modifizieren

Sub ZellentauschTest()
Dim c As Range
Dim w1 As Variant, w2 As Variant
Dim i As Long, a As Long
For Each c In Selection
a = a + 1
Next c
If a  2 Then
MsgBox "Die Anzahl der markierten Zellen ist nicht zwei !" & Chr(10) & _
"Das Makro wird abgebrochen !", , _
"Dezenter Hinweis für " & Application.UserName & ":"
Exit Sub
End If
a = 0
For Each c In Selection
a = a + 1
If a = 1 Then w1 = c.Value
If a = 2 Then w2 = c.Value
Next c
a = 0
For Each c In Selection
a = a + 1
If a = 1 Then c.Value = w2
If a = 2 Then c.Value = w1
Next c
End Sub