#include <bits/stdc++.h>
using namespace std;
int maxscore,minscore,ping[25],sum,maxsum=0;
float max111(int a[],int m){
	maxscore=0;
	minscore=10;
	sum=0;
	for(int i=0;i<m;i++){
	maxscore=max(maxscore,a[i]);
	minscore=min(minscore,a[i]);
	sum=sum+a[i];
	}
	maxsum=max(maxsum,sum-maxscore-minscore);
}
int main() {
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
		cin>>ping[j];}
	    max111(ping,m);	
	}
	printf("%.2f",float(maxsum)/(m-2));
	return 0;
}