Input from keyboard and sub with message - Microprocessor

.MODEL SMALL
.STACK 100H
.DATA
    MSG1 DB 10,13, "ENTER FIRST NUMBER : $"
    MSG2 DB 10,13, "ENTER SECOND NUMBER : $"
    MSG3 DB 10,13, "OUTPUT IS : $"
.CODE
MAIN PROC
    MOV AX,@DATA
    MOV DS,AX

    LEA DX,MSG1
    MOV AH,9
    INT 21H

    MOV AH,1
    INT 21H
    MOV BL,AL

    LEA DX,MSG2
    MOV AH,9
    INT 21H

    MOV AH,1
    INT 21H
    MOV CL,AL


    SUB BL,CL
    ADD BL,48


    LEA DX,MSG3
    MOV AH,9
    INT 21H

    MOV AH,2
    MOV DL,BL
    INT 21H

MAIN ENDP
END MAIN