using namespace std;
double judge(int m)
{
	int max = -1, min = 999;
	int sum=0, tmp;
	double ans;

	for (int i = 1; i <= m; i++)
	{
		cin >> tmp;
		if (max < tmp) max = tmp;
		if (min > tmp) min = tmp;
		sum += tmp;
	}
	sum = sum - max - min;
	ans = 1.0 * sum / (m - 2);
	return ans;
}
int main()
{
	int n, m;
	double ans=-100, tmp;
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
	{
		tmp = judge(m);//计算某一同学评分
		if (ans < tmp)
		{
			ans = tmp;
		}
	}
	cout <<  setprecision(2) << fixed<<ans << endl;
	return 0;