Then you get negative ten plus ten will give you zero. So that works. If this decreases by negative ten and this increases by, say, eleven, then negative ten plus eleven will give you one also positive. So that works. But if we get negative ten, so the system decreases in entropy by negative ten, but the universe increases only by nine, then we get negative ten plus nine will give you negative one, a negative number, a violation of the second law of thermodynamics. And this basically tells us that if the entropy of the system decreases, then the entropy of the surroundings must increase by the same amount or greater.