Option Explicit
Sub test()
Dim derno As Integer
Dim n As Integer
Dim m As Integer
Dim no As String
derno = 0
For n = 1 To Sheets.Count
If Left(Sheets(n).Name, 5) = "Poste" Then
For m = 1 To Len(Sheets(n).Name)
If IsNumeric(Mid(Sheets(n).Name, m, 1)) Then
no = no & Mid(Sheets(n).Name, m, 1)
End If
Next m
If CInt(no) > derno Then derno = no
End If
no = ""
Next n
Sheets("Poste00").Copy after:=ActiveSheet
ActiveSheet.Name = "Poste" & Format(derno + 1, "000")
End Sub