The teachers were all excited about going back to school this year.  They got together for a faculty meeting on the first day and they discovered:

• 17 of the teachers went on a trip during the summer;

• 13 of the teachers taught a class during the summer;

• 15 of the teachers spent some time at the beach.

• Only 2 teachers didn’t go to the beach, or go on a trip, or teach a class all summer.

Some of the teachers did more than one of these activities. 

In fact, 8 teachers went on a trip and were at the beach.  Also, 4 teachers taught a class and went on a trip.  And 1 teacher did all three activities!

How many teachers altogether were at the meeting that first day?