#include<stdio.h>
#include<stdlib.h>
int n, m;
int a[105][25];
double grade[105];
int cmp(const void* x, const void* y)
{
    return *(int*)x - *(int*)y;
}
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            scanf("%d", &a[i][j]);
        }
    }
    for (int i = 0; i < n; i++)
    {
        qsort(a[i], m, sizeof(a[i][0]), cmp);
        for (int j = 1; j < m - 1; j++)
        {
            grade[i] += a[i][j];
        }
        grade[i] /= (m - 2);
    }
    qsort(grade, n, sizeof(grade[0]), cmp);
    printf("%.2lf", grade[n - 1]);
    return 0;
}