How to solve Uva - 11628 - Another lottery?

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I don’t understand why the answer depends only on the last round.

Thank you.

participant wins 2i for every round
so if there are 2 participants and participant 1 wins all previous rounds and loses the m’th round, he would have lesser money
\sum_{i=1}^{m-1} 2i \lt 2m
hence choosing only the last is enough

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What about the case when no one wins the last round ? Won’t we have to judge based on all the other rounds ?

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the number of tickets sold in each round is at least 1…so 1 person has to win