You are blindfolded, and are told if you can correctly solve the following, the blindfold will be removed. You are given 99 coins that are heads up, and an unknown number of coins that are tails up. You never remove the blindfold, you do not peek, …. You can count the coins, put them in arbitrary many piles, flip whichever coins you want, but remember, when you flip and when you sort, you DO NOT know which ones are heads up, which are tails up. In the end, you must end up with just two piles, each containing an equal number of heads. How do you do this?

Communicated by Eric Adelizzi.