#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
int fen[21];
int main() {
	int n, m;
	double ans = 0;
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		int sum = 0;
		for (int j = 0; j < m; j++) {
			cin >> fen[j];
		}
		sort(fen, fen + m);
		for (int j = 1; j < m - 1; j++) {
			sum += fen[j];
		}
		if (sum / (m - 2) > ans) {
			ans = sum / (m - 2);
		}
	}
	printf("%.2lf", ans);
	return 0;
}