#define _CRT_SECURE_NO_WARNINGS 1
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
int n, m, M, MAX = 0;
int a[20];
int main() {
	scanf("%d%d", &n, &m);
	for (int i = 0; i < n; i++) {
		for (int i = 0; i < m; i++) {
			scanf("%d", &a[i]);
		}
		sort(a, a + m);
		M = 0;
		for (int i = 1; i < m - 1; i++) {
			M += a[i];
		}
		MAX = max(M, MAX);
	}
	printf("%.2lf", double(MAX / (m - 2)));
	return 0;
}