#include <stdio.h>
int num1[1000][1000];
int ans[1000];
int d[1000];

double gg(int ans[], int b) {
	for (int i = 0; i < b; i++) {
		int d = ans[i] / (b - 2);
		return d;
	}
}

int main() {
	int a, b, c, max, min;
	scanf("%d %d", &a, &b);
	for (int i = 0; i < a; i++) {
		max = min = num1[i][0];
		for (int j = 0; j < b; j++) {
			scanf("%d", &num1[i][j]);
			if (num1[i][j] > max) {
				max = num1[i][j];
			} else if (num1[i][j] < min) {
				min = num1[i][j];
			}
			ans[i] += num1[i][j];
		}
		ans[i] -= max + min;
	}
	for (int i = 0; i < a; i++) {
		d[i] = gg(&ans[i], b);
		if (i == 0 || d[i] > max) {
			max = d[i];
		}
	}
	printf("%.2lf", double (max));
	return 0;
}