Ideal expiry price for a 35/37.5/40 butterfly

You go long a butterfly built from options struck at $35$ and $40$ (the wings) and $37.5$ (the body). At expiry, what stock price would you most like to see?

$37.5$. A long butterfly is long one option at each wing and short two at the body, so its payoff is a tent that is zero outside $[35,40]$ and peaks at the middle strike.