.data
    msgTemplate db "serial %d", 0
    serial dd ? ; initialize this somewhere

.code
start:
    mov ecx, 222222 

loop_start:
    mov eax, 2 ; c1
    mov ebx, 2 ; c2, etc.

    cmp eax, [serial]
    je match_found

    inc ecx
    cmp ecx, 999999
    jle loop_start

    jmp exit

match_found:
    ; write your msgbox here :)

exit:
    ; do your cleanup