#include<bits/stdc++.h>
using namespace std;
int n,m,a[1001],maxn[1001] = {INT_MIN},minn[1001] = {INT_MAX};
int main(){
	cin >> n >> m;
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= m; j++){
			int w;
			cin >> w;
			a[i] += w;
			maxn[i] = max(maxn[i],w);
			minn[i] = min(minn[i],w);
		}
		a[i] -= maxn[i] + minn[i];
	}
	sort(a + 1,a + 1 + n);
	double v = a[n] / (m - 2) * 1.00;
	printf("%.2lf",v);
	return 0;
}