Вычисление значения выражения (Assembler) a=a*(a+b/4)/(k-1)

.486    
.model flat, stdcall
option casemap: none
 
include /masm32/include/windows.inc
include /masm32/include/user32.inc
include /masm32/include/kernel32.inc
 
includelib /masm32/lib/user32.lib
includelib /masm32/lib/kernel32.lib
 
include /masm32/macros/macros.asm 
uselib masm32, comctl32, ws2_32 
 
BSIZE equ 20
 
.data
 
ConsoleTitle    db 'VVOD, Result', 0
title_1 db 'Произведение', 0
 
.data?  
 buf BYTE BSIZE dup(?)
 stdout DWORD ?
 stdin DWORD ?
 written DWORD ?
 read DWORD ?
 
 a dd ?
 b dd ?
 k dd ?
 
 
.code
start:
call    AllocConsole
invoke  SetConsoleTitle, addr ConsoleTitle
 
invoke GetStdHandle, STD_OUTPUT_HANDLE 
    mov stdout, eax
    invoke GetStdHandle, STD_INPUT_HANDLE
    mov stdin, eax
    invoke ReadConsole, stdin, addr buf, 20, addr read, NULL        
    invoke atol, addr buf
    mov ebx, eax
    
invoke GetStdHandle, STD_OUTPUT_HANDLE 
    mov stdout, eax
    invoke GetStdHandle, STD_INPUT_HANDLE
    mov stdin, eax
    invoke ReadConsole, stdin, addr buf, 20, addr read, NULL        
    invoke atol, addr buf
    mov ecx,eax
 
invoke GetStdHandle, STD_OUTPUT_HANDLE 
    mov stdout, eax
    invoke GetStdHandle, STD_INPUT_HANDLE
    mov stdin, eax
    invoke ReadConsole, stdin, addr buf, 20, addr read, NULL        
    invoke atol, addr buf
       
mov a,ebx
mov b,ecx
mov k,eax
 
mov eax,a
add eax,a
 
 
add eax,b
mov ecx,4
sub eax,ecx
sub eax,k
 
mov ebx,1
sub eax,ebx
mov k,eax
 
    invoke dwtoa, k, addr buf                                
    invoke WriteConsole, stdout, addr buf, read, addr written, NULL    
    invoke  MessageBox, 0, addr buf, addr title_1,MB_OK               
    invoke ExitProcess, 0
 
end start