#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, m, a[100][20];
	double ans[100], tmp;
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		double bg = a[i][0], sm = a[i][0], sum = 0;
		for (int j = 0; j < m; j++) {
			cin >> a[i][j];
			if (bg < a[i][j]) {
				bg = a[i][j];
			}
			if (sm > a[i][j]) {
				bg = a[i][j];
			}
			sum += a[i][j];
		}
		ans[i] = (sum - bg - sm) / (m - 2);
	}
	tmp = ans[0];
	for (int i = 0; i < n; i++) {
		if (tmp < ans[i]) {
			tmp = ans[i];
		}
	}
	printf("%.2f", tmp);
	return 0;
}