#include<stdio.h>
#include<algorithm>
using namespace std;

int score[30] = {};
int main() {
    //输入
    int n,m;
    double ans;
    scanf("%d%d",&n,&m);

    //输入分数
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            scanf("%d",&score[j]);
        }
        sort(score, score + m);
    }
    int sum = 0;
    for (int j = 1; j < m - 1; j++) {
        sum += score[j];
    }
    ans = max(ans, 1.0 * sum / (m - 2));
    
    printf("%.2lf",ans);
    return 0;
}