#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
int n=0,m=0,x=0,b,i,j;
double maxn=0,max1=0,minn=15,sum=0;
cin>>n>>m;
b=m-2;
for(i=1;i<=n;i++){
	maxn=sum=0;minn=15;
	for(j=1;j<=m;j++){
		cin>>x;
		sum+=x;
		if(x>=maxn) maxn=x;
		else if(x<=minn) minn=x;
	}
	sum=sum-maxn-minn;
	sum=sum/b;
	if(sum>max1) max1=sum;
}
printf("%.2f",max1);
return 0;
}