#include<iostream>
#include<iomanip>
using namespace std;
double comp(double brr[], int b);
double score(int brr[], int a);
int main() {
	int n, m,i,j, arr[100] = { 0 };
	double ans[100],answer;
	cin >> n >> m;
		for (i = 0; i < n; i++) {
			ans[i]= score(arr, m);
		}
		answer = comp(ans, n);
		cout << fixed<<setprecision(2)<<answer;
	return 0;
}
double score(int brr[],int a) {
	int i, j,t,sum=0;
	for (i = 0; i < a; i++) {
		cin >> brr[i];
	}
	for (i = 0; i < a - 1; i++) {
		for (j = 0; j < a - i - 1; j++) {
			if (brr[j] > brr[j + 1]) {
				t = brr[j];
				brr[j] = brr[j + 1];
				brr[j + 1] = t;
			}
		}
	}
	for (i = 1; i < a; i++) {
		sum = sum + brr[i];
	}
	return sum / (a - 2) * 1.0;
}
double comp(double brr[], int b) {
	int i;
	double max = 0.0;
	for (i = 0; i < b; i++) {
		if (brr[i ]> max) {
			max=brr[i];
		}
	}
	return max;
}