Calculate A*B-C+D

Whitey was in the fertilized egg business. He had several hundred young layers called pullets and eight or ten roosters, whose job was to fertilize the eggs. Whitey kept records and any rooster that didn't perform went into the soup pot and was replaced.
That took an awful lot of Whitey's time so Whitey got a set of tiny bells and attached them to his roosters.
Each bell had a different tone so Whitey could tell from a distance, which rooster was performing.
Now he could sit on the porch and fill out an efficiency report simply by listening to the bells.
Whitey's favorite rooster was old Brewster, a very fine specimen he was, too. But on this particular morning Whitey noticed old Brewster's bell hadn't rung at all!
Whitey went to investigate. The other roosters were chasing pullets, bells-a-ringing. The pullets, hearing the roosters coming, would run for cover.
BUT, to Whitey's amazement, Brewster had his bell in his beak, so it couldn't ring. He'd sneak up on a pullet, do his job and walk on to the next one.
Whitey was so proud of Brewster, he entered him in the county fair... and Brewster became an overnight sensation among the judges. The result...
The judges not only awarded Brewster the "No Bell Piece Prize" but they also awarded him the "Pulletsurprise" as well.