#include <bits/stdc++.h>
using namespace std;
int n,m,a[21];
double maxscore=INT_MIN;
int main()
{
	cin>>n>>m;
	for(int i=0;i<n;i++)
	{
		int sum=0;
		double average=0;
		for(int j=0;j<m;j++) 
		{
			cin>>a[i];
			sort(a,a+m);
			for(int k=1;k<m-1;k++) sum+=a[k];
			average=sum/(m-2);
			if(average>maxscore) maxscore=average; 
		}
	}
	printf("%.2f",maxscore);
	return 0;
}