#include<iostream>
#include<cmath>
#include<cstring>
#include<iomanip>
using namespace std;
int main()
{
	int m,n,d,f;double ver,ver1,y,u,sum;
	cin>>m>>n;
	double  a[m][n];
	for (d=0;d<m;d++){
		for (f=0;f<n;f++){
			cin>>a[d][f];
		}
	}
	for (d=0;d<1;d++){u=a[d][0];y=a[d][0];sum=0;
		for (f=0;f<n;f++){u=max(u,a[d][f]);
		y=min(y,a[d][f]);
sum=sum+a[d][f];}
ver=(sum-y-u)/(n-2);}
	for (d=1;d<1;d++){u=a[d][0];y=a[d][0];sum=0;
		for (f=0;f<n;f++){u=max(u,a[d][f]);
		y=min(y,a[d][f]);
sum=sum+a[d][f];}
ver1=(sum-y-u)/(n-2);
ver=max(ver,ver1);}
cout<<setiosflags(ios::fixed)<<setprecision(2)<<ver;

return 0;
}