n banks have been robbed this fine day. m (greater than or equal to n) police cruisers are on duty at various locations in the city. n of the cruisers should be dispatched, one to each of the banks, so as to minimize the average time of arrival at the n banks. Input The input file contains several sets of inputs. The description of each set is given below: The first line of input contains 0 < n ≤ m ≤ 20. n lines follow, each containing m positive real numbers: the travel time for cruiser m to reach bank n. Input is terminated by a case where m = n = 0. This case should not be processed. Output For each set of input output a single number: the minimum average travel time, accurate to 2 fractional digits. Sample Input 34 10.0 23.0 30.0 40.0 5.0 20.0 10.0 60.0 18.0 20.0 20.0 30.0 00 Sample Output 13.33