; r0 - state
start:
    mov r0, 0
wait:
    ; wait for switch here
    jmp wait
n:
    inc r0
    jmp check
d:
    inc r0
    inc r0
check:
    mov a, r0
    add a, -3
    jc done
    jmp wait
done:
    ; open door here
    jmp start