3. Xiao Li and Xiao Zhang are running at a constant speed on a circular track. They start from the same place at the same time. Xiao Li runs clockwise and completes a lap every 72 seconds, while Xiao Zhang runs counterclockwise and completes a lap every 80 seconds. At the start, Xiao Li has a relay baton, and each time they meet, the baton is passed from one to the other (the time taken for passing the baton is negligible). The relay baton returns to the starting point in the minimum of $\qquad$ seconds.