#include<bits/stdc++.h>
using namespace std;
int a[10001],n,m;
double q,ans,x,minn=1e9,maxx;
int main()
{
    cin>>n>>m;
    for(int i=1; i<=n; ++i)
	{
        for(int j=1; j<=m; ++j)
		cin>>x,ans+=x;
		minn=min(x,minn);
		maxx=max(maxx,x);
        ans=ans-minn-maxx;
        ans=1.0*ans/(1.0*(m-2));
        if(ans>q) q=ans;
        ans=0;
        minn=1e9;
    }
    printf("%.2f",q);
    return 0;
}