sm05-2

    .text
    .global main
main:
    push {lr}
solve:
    ldr r3, =stdin
    ldr r3, [r3]
    mov r0, r3
    bl fgetc
    cmp r0, #-1
    beq end
    cmp r0, #48
    blt solve
    cmp r0, #58
    bge solve
    ldr r3, =stdout
        ldr r3, [r3]
    mov r1, r3
    bl fputc
    b solve
end:
    pop {lr}
    mov r0,#0
    bx lr