Smallest number of items from given probability

Hey All,

Another problem I'm confused with.

A bag contains several blue discs and several yellow discs. Find the smallest number of discs which should be taken out of the bag, if the probability that at least 3 of those removed are of the same color is 1.

Only thing I can see is that least number must be > 3. How do I proceed if the no of items is unknown. I have feeling I am missing something simple, a hint would be great.

Thanks again for all your help!