At a Christmas party, the teacher asks students to take out $$2$$ glass balls from a bag with many glass balls in it. These glass balls are exactly the same in shape, size and texture. But they are in $$5$$ different colors as red, yellow, white, blue and green (students cannot see the color before they take balls out). There is an interesting finding: there are always $$2$$ people who have taken out the same kind of balls. There are at least~\uline{~~~~~~~~~~}~people who participate this activity. 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations->Basic Operations of Combinations