A to B to C
A goes to B's shop and buys a toy for $200. A gives B $1000. B doesn't have change, and goes to C. B and C exchange $1000, and B gives A the $800 he owes. Later, C realizes that the money B gave is fake and goes to B, demanding his money back. B realizes that the fake money was what A gave him, but still gave C $1000 back. How much money did B lose?