.model tiny

.data
  str1 db 10," INSERISCI LETTERA => $"
  str2 db 10," LETTERA PRECEDENTE => $"

.code
  org 0100h

main:
  mov dx, offset str1
  mov ah, 9
  int 21h

  mov ah, 1
  int 21h

  sub al, 01h

  mov dx, offset str2
  mov ah, 9
  int 21h

  mov ah, 2
  mov dl, al
  int 21h

  mov ah, 4ch
  int 21h
end main