'str.length only returns a maximum of 20 (vb.net)

So basically I'm trying to get the length of an input of numbers. The following code runs but it only goes up to 20, after that it displays a length of 20 for any length of string that exceeds 20.

Can anyone help?

If index = 3 Then
    'BASE 2 to 10 CONVERSION SELECTED'
    output = ""
    Dim length As Integer = CStr(input).Length
    If length > 15 Then
        length = length - 3
    Else
        length = length - 1
    End If
    MsgBox(length)
End If


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