#include<iostream>
#include<iomanip>
#include<sstream>
#define MAXN 103
using namespace std;
short score1[MAXN][MAXN];
double score(int n,int m)
{
	stringstream in;
	int a,b,sum=0,max=0,min=11;
	double c;
	for(b=1;b<=m;b++)
	{
		cin>>score1[n][b];
		sum+=score1[n][b];
		if(score1[n][b]>max)
		max=score1[n][b];
		if(score1[n][b]<min)
		min=score1[n][b];
	}
	sum-=max;
	sum-=min;
	in<<fixed<<setprecision(2)<<sum/(m-2);
	in>>c;
	return c;
}
int main()
{
	int n,m,a;
	double c,max=0;
	cin>>n>>m;
	for(a=1;a<=n;a++)
	{
		c=score(a,m);
		if(c>max) max=c;
	}
	cout<<fixed<<setprecision(2)<<max;
	return 0;
}