Try this code:
Sub save()
Dim pres As Presentation
Dim var1 As String
var1 = InputBox("geef hier je maand aan")
If var1 <> "" Then
For Each pres In Application.Presentations
pres.SaveAs "X:\SSC_HR\SENS\Bedrijfsbureau\Rapportages\SENS referenten rapportage\Template_Uploaden\" & Split(pres.Name, ".")(0) & var1 & ".ppt"
Next
End If
End Sub