How can I write this assembly 8086 program?

Write a program in assembly 8086 language that ask the user to input a number. If the character read is '0' it executes a + 3, otherwise if it is '1' it executes a-3 otherwise (if different from '0' and '1') it prints the character 'E' on the screen. The variable 'a' is 16 bits long and initialized at 15h 

.model small 

.stack 100h

.data 
num db ?
num1 db 15h
msg1 db "Inserisci un numero... $"
msg2 db "24 $"
msg3 db "18 $"
msg4 db "Premere un tasto per uscire... $"

.CODE
	mov ax, @data 
	mov ds,ax 
	
	lea dx, msg1
	mov ah, 09h      ;output
	int 21h
	
	mov ah, 01h      ;input
	int 21h
	and al, 0Fh     
	mov num, al     
	
	call newLine
	
	CMP num, 00
	je numUguale1
	
	mov ah, 09h
	
	lea dx, msg2
	mov ah, 09h     
	int 21h
	
	mov ah, 01h    
	int 21h
	
	call newLine
	
	jmp fine
	
numUguale1:
	lea dx, msg3
	mov ah, 09h     
	int 21h
	
	mov ah, 01h
	int 21h        
	
	mov ax, 4c00h  
	int 21h
	
	call newLine
	
fine:
    lea dx, msg4	
	mov ah, 09h     
    int 21h
	
	mov ah, 01h
    int 21h        
	
	mov ax, 4c00h  
	int 21h
	
	call newLine
	
newLine:
	mov ah, 02h
	mov dl, 0Ah
	int 21h
	
	mov ah, 02h
	mov dl, 0Dh
	int 21h
	
	ret
END