Xiaohua and Xiaoming set off from places a and b at the same time, and meet each other in 60 minutes. Xiaohua arrives at point b and returns to chase Xiaoming. After 20 minutes, Xiaohua catches up with Xiaoming. Xiaohua then walked to point b and then returned to meet Xiaoming. So on and so forth. How many times did Xiao Hua catch up with Xiao Ming when Xiao Ming returned to land a?
小华和小明同时从a、b两地相对出发，60分钟相遇，小华到达b地并返回追小明，经过20分钟小华追上小明．小华接着向b地走再返回遇到小明．依此类推．问小明回到a地时小华追上小明几次？
<result>3</result>