Quoting to someone who knows

You make a market on a contract that pays, in dollars, the roll of a fair six-sided die. You'll buy one contract at $3 (your bid) or sell one at $4 (your ask). One trader comes along who has already seen the roll. They buy from you at $4 if the roll is above 4, sell to you at $3 if the roll is below 3, and otherwise don't trade. After any trade, the contract settles at the roll. What is your expected profit, in dollars, per roll?