#include<bits/stdc++.h>
using namespace std;
struct a{
	double b[21];
}c[101];
int main(){
	int n,m,x;
	double he=0;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		int d=0;
		for(int j=1;j<=m;j++){
			cin>>c[i].b[j];
			d+=c[i].b[j];
		}sort(c[i].b+1,c[i].b+1+m);
		d=(d-c[i].b[1]-c[i].b[m])/(m-2);
		if(d>he)he=d;
	}printf("%.2lf",he);
return 0;
}