Zou and Chou are practicing their 100-meter sprints by running 6 races against each other. Zou wins the first race, and after that, the probability that one of them wins a race is 2/3 if they won the previous race but only 1/3 if they lost the previous race. The probability that Zou will win exactly 5 of the 6 races is m/n where m and n are relatively prime positive integers. Find m+n.