Let m,n be positive integers greater than 1. We define the sets P_m={1/m, 2/m, ..., (m-1)/m} and P_n={1/n, 2/n, ..., (n-1)/n}.

Find the distance between P_m and P_n, that is defined as min{|a-b|: a∈P_m, b∈P_n}