#include<iostream>
#include<algorithm>
using namespace std;
void asort(int a[], int N)
{
    int i, j;
    for (i = 0; i < N - 1; i++) { //控制n-1趟冒泡
        for (j = 0; j < N - 1 - i; j++)
        {
            if (a[j] > a[j + 1]) { //比较相邻的两个元素
                int tmp; //临时变量
                tmp = a[j]; //交换
                a[j] = a[j + 1];
                a[j + 1] = tmp;
            }
        }
    }
    
}

int main()
{
    int n, m, sum[100] = { 0 };
    double av[100] = { 0 }, maxa = 0;
    cin >> n >> m;
    int a[100][20] = { 0 };
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            cin >> a[i][j];
            sum[i] += a[i][j];

        }
        asort(a[i], m);

    }for (int i = 0; i < n; i++) {
        sum[i] -= (a[i][0] + a[i][m - 1]);
        av[i] = sum[i] / (m - 2);
        maxa = max(av[i], maxa);
    }
    printf("%.2lf", maxa);
    return 0;
}