File 1
Show1
Show2
Show3
Show4
Show5
File2
Advert1
Advert2

Show1
Advert1
Show2
Advert2
Show3
Advert1
Show4
Advert2
Show5

For k := 0 to StringlistAdvert.Count - 1 do
 Begin
     StringListFinal.Add(StringlistShow[k]);
     StringListFinal.Add(StringListAdvert[k]);
     StringlistAdvert.Delete(k)
 End;