#include<stdio.h>
int main() {
	int a[20][100], n, m;
	float sum[20], max = 0.0;
	scanf(" %d %d", &n, &m);
	for (int j = 0; j < n; j++) {
		for (int i = 0; i < m; i++) {
			scanf("%d", &a[j][i]);
		}
		for (int i = 0; i < m; i++) {
			if (a[j][i] > a[j][i + 1]) {
				int temp = a[j][i];
				a[j][i] = a[j][i + 1];
				a[j][i + 1] = temp;
			}
		}
		for (int i = 1; i < m - 1; i++) {
			sum[j] += a[j][i];
		}
		if (sum[j] > max) {
			max = sum[j];
		}
	}
	printf("%.2f", (max / (m - 2)));
	return 0;
}