#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <stdlib.h>
int cmp(const void* e2, const void* e1)
{
	return ((float*)e1)[0] - ((float*)e2)[0];
}
int main()
{
	int n = 0;
	int m = 0;
	scanf("%d%d", &n, &m);
	float arr[100][20] = { 0 };
	float sum[100] = { 0 };
	float ave[100] = { 0 };
	int i = 0;
	int j = 0;
	for (i = 0; i < n; i++)
	{
		for (j = 0; j < m; j++)
		{
			scanf("%f", &arr[i][j]);
		}
	}
	for (i = 0; i < n; i++)
	{
		qsort(arr+i,m,sizeof(float),cmp);
	}
	for (i = 0; i < n; i++)
	{
		for (j = 1; j < m-1; j++)
		{
			sum[i] += arr[i][j];
		}
		ave[i] = sum[i] / (m - 2);
	}
	qsort(ave, n, sizeof(float),cmp);
	printf("%.2f", ave[0]);
}