What's the maximum amount we can earn from this situation?
First bookmaker, is offering to give us 100 euros after our first bet of 200 euros. It doesn't matter if we win or lose our bet, it's an extra that will add to our profit or loss. The only restriction we have is that we need to bet on an event that has odds higher than 2 (decimal).
Second bookmaker, (this is an optional step), we can consider to bet against the outcome we chose in the first bookmaker in order to always show a profit. But does this lower our expected value?