#include<iostream>
#include<iomanip>
using namespace std;
double Grade(int m, double arr[]) {
	for (int i = 0; i < m; i++) {
		cin >> arr[i];
	}
	for (int i = 0; i < m - 1; i++) {
		for (int j = 0; j < m - 1 - i; j++) {
			if (arr[j] > arr[j + 1]) {
				double temp = arr[j];
				arr[j] = arr[j + 1];
				arr[j + 1] = temp;
			}
		}
	}//冒泡升序排序
	double sum = 0;
	for (int i = 1; i < m - 1; i++) {
		sum += arr[i];
	}
	double average = sum / (m - 2);
	return average;
}//计算平均值
int main() {
	int n, m;

	cin >> n >> m;
	double max = 0;
	for (int i = 0; i < n; i++) {
		double arr[110];
		for (int j = 0; j < m; j++)
			cin >> arr[j];
		double score = Grade(m, arr);
		max = max > score ? max : score;//比较最大值
	}
	cout << fixed << setprecision(2) << max;
	return 0;
}