I am on the phone with my brother. We are arguing about who has to pay some bill of our parents. We agree to toss a coin. We are talking on the phone and I know he can't see me so I could cheat but (for once) I don't. We agree that whoever gets heads after the third toss, after two heads has to pay. I called heads. What are my chances of having to pay ?

Answer as a probability to three decimal places.