Shortest command to calculate the sum of a column of output on Unix?

ipcs -mb | tail +4 | awk '{ sum += $7 } END { print sum }'

Or without tail:

ipcs -mb | awk 'NR > 3 { sum += $7 } END { print sum }'

Using awk with bc to have arbitrary long results (credits to Jouni K.):

ipcs -mb | awk 'NR > 3 { print $7 }' | paste -sd+ | bc