#include<algorithm>
using namespace std;
int main()
  {
  	short n,m;
   double max=-0.1;
	cin>>n>>m;
	short a[m];
	for(int i=0;i<n;i++)
	{short x=0;
		for(int j=0;j<m;j++){cin>>a[j];x+=a[j];}
		sort(a,a+m);
		short fen=x-a[0]-a[m-1];
		if(fen/(m-2)>max)max=fen/(m-2);
	}
	printf("%.2f",max);
}