其它
$$100$$ squares are placed in a row, each filled up with a digit among $$0$$, $$1$$, $$2$$, $$\cdots $$, $$9$$. Now if a digit appears $$5$$ times or more, all the squares filled up with that digit will be painted red. Find the smallest possible number of red squares. 
Overseas Competition->Knowledge Point->Combinatorics->Pigeonhole Principle
B 