AutoCAD Inventor :: How To Stop The Code In Middle Of Process

I am using ilogic to modify the boxes:

I have a one rectangular box in that box again small rectangular boxes in this my problem is when iam giving value for smaller boxes(all boxes height) more than outer box how it will show the message box and how to stop the code.

d1=big box height
d2,d3,d4---small boxes height

I am writing code like this:

IF((d2+d3+d4)=<d1) then
Msg.box(give correct value)
end if

here it's showing the message and it,s not stoping the program.