#include<iostream>
using namespace std;
int n,m,maxf=0,minf=0,a[100001][100001],s=0;
double b[100001],t=0.0;
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			cin>>a[i][j];
			if(maxf>a[i][j])
			{
				maxf=a[i][j];
			}
			if(minf>a[i][j])
			{
				minf=a[i][j];
			}
			s+=a[i][j];
		}
		b[i]=(s-maxf-minf)/(m-2);
        s=0;
	}
	for(int i=1;i<=n;i++)
	{
		if(b[i]>t)
		{
			t=b[i];
		}
	}
	printf("%.2f",(double)t);
}