#include <iostream>
#include<cstdio>
using namespace std;
int m, n, sum = 0;
double gr() {
	int max_ = -1, min_ = 11, sum = 0,x;
	double avr=0;
	for (int i = 0; i < m; i++)
	{
		cin >> x;
		sum += x;
		if (x > max_) {
			max_ = x;
		}
		else if (x < min_) {
			min_ = x;
		}
	}
	avr = 1.0 * (sum - max_ - min_) / (m - 2);
	return avr;
}
int main()
{
	double MAX = 0;
	cin >> n >> m;
	for (int i = 0; i < n; i++)
	{
		int t = gr();
		if (t> MAX) MAX =t;
	}
	printf("%.2f", MAX);
	return 0;
}