import java.util.Scanner;
import java.util.Arrays;
public class Main {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        int[] arr = new int[m];
        int score = 0;
        double a=0.00,b=0.00;        
        for(int i=0;i<n;i++) {
            for(int j=0;j<m;j++) {
                   arr[j] = scanner.nextInt();
            }
            Arrays.sort(arr);
            for(int j=1;j<arr.length-1;j++) {
                    score+=arr[j];
            }     
                   if(i==0) {
                   a = (double)score/(m-2);
                   }else if(i>0) {
                       b = (double)score/(m-2);
                       if(a<b) {
                           a = b;
                       }
                   }
                   score = 0;
        }
        System.out.printf("%.2f",a);
    }

}