#include<bits/stdc++.h>

using namespace std;
int a[105][25];int ma[105];int mi[105];double pj[105];
int main(){
	int n,m;
	cin>>n>>m;
	
	for(int i=1;i<=100;i++){
		ma[i]=-1;
		mi[i]=123;
	}
	
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>a[i][j];
			if(mi[i]>a[i][j] ) mi[i]=a[i][j];
			if(ma[i]<a[i][j])ma[i]=a[i][j];
		}
		
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(a[i][j]!=ma[i]&&a[i][j]!=mi[i])pj[i]+=a[i][j];
		}
		pj[i]/=(m-2);
		
	}
	double mini=-890;
	for(int i=1;i<=n;i++){
		if(mini<pj[i])mini=pj[i];
	}
	cout<<fixed<<setprecision(2)<<mini*1.000;
	return 0;
}