Trying to calculate school attendance in Excel 2010

If I'm right in thinking G2 is your flag then the formula to make it a count would be:

=MAX(0,SUM(E2:F2)-6)

How do we tell how many detentions have been served?

The detentions served will be submitted to school administration physically, so a formula will be needed to be able to decrease the number in the new column. Is that even possible? I was thinking that one of the unexcused absences could be changed so the count in the new column would decrease. Thanks so much for your help with this.