There is a box which have 33 yellow marbles and 35 green marbles. You also have 34 green marbles outside the box.
Randomly remove two marbles from the box.
* If they are of different colors, put the yellow one back in the box.
* If they are the same color, take them out and put a green marble back in the box.
Repeat this until only one marble remains in the box.
What is the color of the sole marble left in the box ?