#include<bits/stdc++.h>
using namespace std;
const int N = 105;
int a[N];
double b[N];
int n, m;
double aver(int a[],int m) {
    int sum=0;
	sort(a, a + m);
	for (int i = 1; i < m-1; i++) {
		sum += a[i];
	}
	double t=sum/(m-2);
	return t;
}
int main() {
	scanf("%d%d", &n, &m);
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			scanf("%d", &a[j]);
		}
		b[i] = aver(a,m);
	}
	sort(b, b + n);
	printf("%.2lf", b[n-1]);
	return 0;
}