#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<queue>
#define ll long long
using namespace std;
int n,m,a[200][200],maxx=0,minn=100;
double b,ans;
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			cin>>a[i][j];
			b+=a[i][j];
			if(maxx<a[i][j]) maxx=a[i][j];
			if(minn>a[i][j]) minn=a[i][j];
		}
		b=(b-maxx-minn)/(m-2);
		if(b>ans) ans=b;
		b=0;
	}
	printf("%.2f",ans);
	return 0;
}