.text
.global main
main:
    push {lr}

again:
    ldr r0, =stdin
    ldr r0, [r0]
    bl fgetc(PLT)
    cmp r0, #-1
    beq end

    cmp r0, #'0'
    blt again
    cmp r0, #'9'
    bgt again

    ldr r1, =stdout
    ldr r1, [r1]
    bl fputc(PLT)
    b again

end:

    pop {lr}
    bx lr
.word stdin
.word stdout