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

20分