Add border & apply conditional formatting to sheets based on cell value

Hi all,
I have a macro that applies borders and conditional formatting to a sheet based on a cell value. The Workbook has 20+ worksheets and the sheet names may change. I am looking for a macro that will apply the below code it to all worksheets except for 'Sheet1', 'Sheet2' and 'Sheet3'.

    Sheets("Sample").Select
    If Range("A3").Value > "0" Then Call add
    .
    .

Sub add()

'add border
    Cells.Select
    Selection.Borders.LineStyle = xlNone
    Range("A2").Select
    Range(Selection, Selection.End(xlToRight)).Select
    Range(Selection, Selection.End(xlDown)).Select
    With Selection.Borders
        .LineStyle = xlContinuous
        .Weight = xlThin
        .ColorIndex = xlAutomatic
    End With
    
'apply conditional formatting

    Range("A3:U3").Select
    Range(Selection, Selection.End(xlDown)).Select
    Selection.FormatConditions.Add Type:=xlExpression, Formula1:= _
        "=MOD(ROW(),2)=0"
    Selection.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
    With Selection.FormatConditions(1).Interior
        .PatternColorIndex = xlAutomatic
        .ThemeColor = xlThemeColorLight2
        .TintAndShade = 0.799981688894314
    End With
    Selection.FormatConditions(1).StopIfTrue = False

End Sub

I believe that the code I am looking for, has to start w/

Dim ws As Worksheet
For Each ws In ActiveWorkbook.Worksheets

but I don't know how to adjust the above code.

Any help is much appreciated.

Thanks