#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,m,maxn,minn,a;
	double s,maxnn;
	cin>>n>>m;
	for(int i=0;i<n;i++){
		s=0;
		maxn=-1;
		minn=11;
		for(int j=0;j<m;j++){
			cin>>a;
			maxn=max(maxn,a);
			minn=min(minn,a);
			s+=a;
		}
		s-=maxn+minn;
		s=s/(m-2);
		if(maxnn<s)maxnn=s;
	}
	cout<<fixed<<setprecision(2)<<maxnn;
	return 0;
}

懒得说什么，不会的就讨论一下