Check if Excel cell is not number

[Einsener37]

Hi!
I'm trying to check if cell in excel isn't a number.
But it gives me error.
What seems to be issue?

Sub isNotNr()
    Dim input As Single
    Dim WS As Worksheet
    Set WS = ThisWorkbook.Worksheets("Sheet1")
    input = WS.Range("B18").Value
    Range("B18").Select
    If input = 0 Or input < 0 Or IsNumeric(input) = False Then
      MsgBox "Check input"
      Exit Sub
     End If
End Sub

Thanks!