#include<iostream>
#include<iomanip>
using namespace std;
int main() {
	double n, m, ma, mi, MA = -1, s;
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		double a[20];
		s = 0,ma=0,mi=10;
		for (int j = 0; j < m; j++) {
			cin >> a[i];
			ma = max(ma,a[i]);
			mi = min(mi,a[i]);
			s += a[i];
		}
		s -= ma + mi;
		 MA = max(MA, s);
	}
	cout <<fixed<<setprecision(2)<< MA / (m - 2);
}