#include<stdio.h>
struct stu
{
	double max;
	double min;
	double sum;
	double average;
};
struct stu score[300];
int main()
{
	int array[300][300] = { 0 };
	int n = 0;
	int m = 0;
	scanf("%d%d", &n, &m);
	for (int y = 0; y < n; y++)
	{
		for (int x = 0; x < m; x++)
		{
			scanf("%d", &array[y][x]);
		}
	}
	double max = score[0].average;
	for (int y = 0; y < 7; y++)
	{
		score[y].sum = 0;
		score[y].min = array[y][0];
		score[y].max = array[y][0];
		for (int x = 0; x < m; x++)
		{
			if (score[y].max < array[y][x])
				score[y].max = array[y][x];
			else if (score[y].min > array[y][x])
				score[y].min = array[y][x];
			score[y].sum += array[y][x];
		}
		score[y].average = (score[y].sum - score[y].max - score[y].min) * 1.0 / (m - 2);

		if (max < score[y].average)
			max = score[y].average;
	}
	printf("%.2lf", max);
}