Gluttony's Devouring Ooze

Gluttony's Devouring Ooze enters the battlefield with X +1/+1 counters on it, where X is the total number of cards in all players' hands. At the beginning of your upkeep, you may sacrifice another creature. If you do, put a number of +1/+1 counters on Gluttony's Devouring Ooze equal to the sacrificed creature's power.