#include<bits/stdc++.h>
using namespace std;
int n,m,nm[21];
double maxmid=-1;
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		int maxx=-1,minn=101,mid=0,sum=0;
		for(int j=1;j<=m;j++)
		{
			cin>>nm[i];
			if(maxx<nm[i])
			{
				maxx=nm[i];
			}
			else if(minn>nm[i])
			{
				minn=nm[i];
			}
			sum+=nm[i];
		}
		mid=(sum-minn-maxx)/(m-2);
		if(maxmid<mid)
		{
			maxmid=mid;
		}
	}
	printf("%.2f",maxmid);
}