International Mathematical Olympiad 2010 Problem 5
In each of six boxes there is initially one coin. There are two types of operation allowed:
Type 1: Choose a nonempty box with . Remove one coin from and add two coins to .
Type 2: Choose a nonempty box with . Remove one coin from and exchange the contents of (possibly empty) boxes and .
Determine whether there is a finite sequence of such operations that results in boxes being empty and box containing exactly coins. (Note that .)