Code in ra tên sách 2 lần

[Gia_Khiem (Nguyễn Phạm Gia Khiêm)]

Sao nó in ra tên sách đến 2 lần vậy ạ?

include \masm32\include\masm32rt.inc
.data
    luachon dd ?
    tensach dd ?
  .code

menu_f proc
    print chr$("+------------- menu -----------+",13,10)
    print chr$("|                              |",13,10)
    print chr$("|       1. Nhap ten sach       |",13,10)
    print chr$("|                              |",13,10)
    print chr$("|       2. Hien sach           |",13,10)
    print chr$("|                              |",13,10)
    print chr$("|       3. thoat               |",13,10)
    print chr$("|                              |",13,10)
    print chr$("+------------------------------+",13,10)
    call enter_f
ret
menu_f endp

enter_f proc
    mov luachon, sval(input(" Nhap lua chon cua ban: "))
    call ex_f
    
ret
enter_f endp


ex_f proc
    cmp luachon,1
    je op1

    cmp luachon,2
    je op2

    cmp luachon,3
    je op3

    op1:
        call addbook_f

    op2:
        call showbook_f

    op3:
        jmp thoat
   ret
ex_f endp

addbook_f proc
        mov tensach,input(" Vui long nhap ten sach: ")
        print chr$(13,10)
        call showbook_f
        ret
addbook_f endp

showbook_f proc
    print chr$(" Ten sach ban vua nhap la: ")
    print tensach
    ret
showbook_f endp

    start:
        call menu_f
        thoat:

    exit


end start