#include <bits/stdc++.h>
using namespace std;

struct name{
	int x;
}a[1100],d[1100];

bool cmp(name a,name b){
	return a.x < b.x;
}

int main()
{
	int n,m;cin >> n >> m;
	for(int i = 1;i <= n;i ++){
		int sum = 0;
		for(int j = 1;j <= m;j ++)
			cin >> a[j].x;
		sort(a + 1,a + 1 + m,cmp);
		for(int j = 2;j <= m - 1;j ++)
			sum += a[j].x;
		d[i].x = (double(sum) / double(m - 2));
	}
	sort(d + 1,d + 1 + n,cmp);
	printf("%.2f",(double)(d[n].x));
	
	
	return 0;
}