#include<cstdio>
#include<algorithm>
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=max(a[i],minscore);
		sum +=a[i];
	}
	maxsum=max(maxsum,sum-maxscore-minscore);
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++)
		    scanf("%d",&s[j]);
		stat(s,m);
	}
	printf("%.2f",double(maxsum)/(m-2));
	return 0;
}