Correcting the equation preventing the entry of any quantity for a particular item as long as the remaining balance is equal to 5

[Hany ali]

Hello My Dear ,I Want Correcting the equation preventing the entry of any quantity for a particular item as long as the remaining balance is equal to 5 From Data Validation
In Column B From Input Sheet

=IF(SUMIF(Main!$B:$B,$A2,Main!$F:$F)<=5,"",IF(SUMIF(Main!$B:$B,$A2,Main!$F:$F)-5>=5,$F2-5,$B2))

because i Want To PREVENT Any Quantity For Any Items if it Balance = 5

 

[Hany ali]

Up Please