A Title I Can't Remeber

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I read a book when I was in middle school, though for the life of me I can't remember the title.

I only remember the whole story hazily, it was about a little boy in Russia shortly after the revolution. In particular I remember two scenes: one where the boy is talking to a distant relative, the relative hands him a pebble and says, "This rock will turn to gold, so long as you don't think of camels." And another where he passes another boy on the road with his uncle, the boy on the road isn't moving and so the main character goes to move him, at which point his uncle instructs him to just let the boy be, and he walks away as he freezes to death. In another moment he is talking about soup and how the KGB took his relatives away.

Could /lit/ help me rediscover the title of the book? I've been looking for years