#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,m,sco[105];
	double ans,maxnn=0.00;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		int tot=0,maxn=0,minn=0;
		for(int j=1;j<=m;j++){
			cin>>sco[i];
			if(sco[i]>maxn) maxn=sco[i];
			if(sco[i]<minn) minn=sco[i];
			tot+=sco[i];
		}
		tot=tot-maxn-minn;
		ans=tot/(m-2);
		if(ans>maxnn) maxnn=ans;
	}
	cout<<fixed<<setprecision(2)<<maxnn;
	return 0;
}