Ask after a run of buys

A contract is worth $100$ with probability $0.4$ and $40$ with probability $0.6$. Each arriving trader is informed with probability $0.5$, in which case the trader buys when the value is $100$ and sells when it is $40$. Otherwise the trader is uninformed and buys or sells with probability $0.5$ each. The first $2$ orders were both buys. The market maker now sets the ask for the next order so that its expected profit, if it is a buy, is exactly zero. What is the ask? Give an exact fraction.

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