[8086 ASM] Simple I/O and summation

; given a string over std inpput calculate sum of multiplies of 5 smaller or equal of it
; eg: 34 gives => sum = 30 + 25 + 20 + 15 + 10 + 5 = 105

.data
input DB ?
sum DB ?

.code

org 100h

start:
mov ah, 01h
int 21h
mov input, ah
mov si, input ;si points to string

loopStringToInt:

    lodsb                      ;load the first byte pointed by ESI in al

    cmp al,'0'                 ;check if it's an ascii number [0-9]
    jb noascii                 ;not ascii, exit
    cmp al,'9'                 ;check the if it's an ascii number [0-9]
    ja noascii                 ;not ascii, exit

    sub al,30h                 ;ascii '0' = 30h, ascii '1' = 31h ...etc.
    cbw                        ;byte to word
    push ax
    mov ax,bx                ;bx will contain '12345' in hexadecimal
    mov cx,10
    mul cx                    ;AX=AX*10
    mov bx,ax
    pop ax
    add bx,ax
    jmp loopStringToInt             ;continue until ESI points to a non-ascii [0-9] character
    noascii:
    ret                        ;bx contains integer now

loopFives:
mov cx, 5 ; seed value = 5
cmp bx, cx ; has cx reached bx yet?
jna printsum ;if so print and pass operation back to OS
add sum, cx ; if not, increase sum
add cx, 5 ; get next multiply of 5
jmp loopFives ;; continue loop

printsum:
    mov dl, sum
    mov ah, 02h
    int 21h
int 27h
end start