a ss:sp - 10
 mov dx, 21
 in al, dx
 .
r v0 := aao - (sp - 10)
s cs:100 length bxcx range ss:sp - 10 length v0
if (src == 0) then goto :error
f cs:sro length v0 90
goto :eof
:error
; Waste loop input instruction not found