There are three matchboxes in front of you. One contains two black marbles, the second, two white marbles and the third one has a black and a white marble inside. Each box had the correct label on it until some pesky kid switched them around so that each matchbox is now wrongly labelled.

You can take one marble at a time from any box without looking inside. How many marbles must you remove to be sure of correctly identifying all 3 boxes?