Serial number in all sheets excel macros

Sub Serial_number()
On Error Resume Next

Dim tot_Sheets As Integer
tot_Sheets = Application.Sheets.Count
Dim s As Integer
For s = 1 To tot_Sheets
'Sheets(ActiveSheet.Index + 1).Activate
If s <> 0 Then Sheets(s).Activate
'----------------serial number on sheets----------------
'Check last row_number for a filled cell in sheets
Dim colName As String
colName = "A"
Dim LastCell As Integer
LastCell = Sheets(s).Range(colName & ":" & colName).SpecialCells(xlCellTypeLastCell).Row
'insert a new column to assign serial number
Sheets(s).Columns("A:A").Insert Shift:=xlToRight, _
CopyOrigin:=xlFormatFromLeftOrAbove
'----------------------
'assigning serial number
Dim j As Integer
Dim i As Integer
j = LastCell
For i = 1 To j
Sheets(s).Range("A" & i + 1).Value = i
Next i
Dim c As Integer
Sheets(s).Range("A" & i).Delete
'-----------------------
Next s
End Sub