#include<bits/stdc++.h>
using namespace std;
int n,m;
int a[105][25];
int sum[105];
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		int maxn=-1;
		int minn=11;
		for(int j=1;j<=m;j++){
			cin>>a[i][j];
			minn=min(minn,a[i][j]);
			maxn=max(maxn,a[i][j]);
			sum[i]+=a[i][j]; 
		}
		sum[i]=sum[i]-maxn-minn;
	}
	int mx=-1;
	for(int i=1;i<=n;i++){
		mx=max(mx,sum[i]);
	}
	cout<<fixed<<setprecision(2)<<double(mx/(m-2));
	return 0;
}