#include<stdio.h>
int a[101][21];
double ans[1000];
int maxs(double arr[], int len)
{
	double max = arr[0];
	for (int i = 0; i < len; i++)
	{
		if (arr[i] > max)
		{
			max = arr[i];
		}
	}
	return max;
}
void px(int arr[],int len)
{
	int tmp;
	for (int i = 0; i < len-1; i++)
	{
		for (int j = i + 1; j < len; j++)
		{
			if (arr[i] > arr[j])
			{
				tmp = arr[i];
				arr[i] = arr[j];
				arr[j] = tmp;
			}
		}
	}
}
int main()
{
	int n, m;
	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++)
	{
		px(a[i], m);
	}
	for (int i = 0; i < n ; i++)
	{
		int sum = 0;
		for (int k = 1; k < m - 1; k++)
		{
			sum += a[i][k];
		}
		ans[i] = 1.0 * sum / (1.0 * (m - 2));
	}
	double ret = maxs(ans, n);
	printf("%.2lf", ret);
	return 0;
}