mov ax,3
mov bx,0
mov ecx,X
mov dx,1
int 80h

mov cx,word[X]
xor cx,1
mov word[X],cx

mov eax,4
mov ebx,1
mov ecx,X
mov edx,1
int 80h

mov eax,1
mov ebx,0
int 80h

X dw 0