In a game, a person flips a fair coin twice, and based on the number of heads observed, he will be allowed to shoot so many times (equal to the number of heads observed) on a target. Assume the probability of hitting a target in one shot is 0.25. If the person obtained two heads, what is the probability of hitting the target only once? [The answer should be a number rounded to five decimal places, don't use symbols such as %]