There are $$6$$ footballs, $$9$$ basketballs and $$3$$ volleyballs in the playground. Lily will be blindfolded before she takes the balls out, one at a time. How many balls must Lily take out such that she can get $$6$$ balls of the same type? 
Overseas Competition->Knowledge Point->Combinatorics->Pigeonhole Principle->Worst Case in Pigeonhole Principle Problems