#include <stdio.h>

int main(){
    int x[100][20];
    int n,m,max, min;
//输入
    scanf("%d %d",&n ,&m);
    for (int i = 0;i < n;i++){
        for (int j = 0;j < m;j++){
            scanf("%d",&x[i][j]);
        }
    }

    int y[20];
    double total[100];
    int num = 0;

    for (int j = 0;j < n;j++){
        for (int i = 0;i < m;i++){
            y[i] = x[j][i];
            num += y[i];
        }
        min = max = y[0];
        for (int k = 1;k < m;k++){
            if (max > y[k])
                max = y[k];
        }
        for (int k = 1;k < m;k++){
            if (min < y[k] && y[k] != 0)
                min = y[k];
        }

        total[j] = (double)(num - max - min) / (m - 2);
    }

    double max2;
    max2 = total[0];
    for (int k = 1;k < m;k++){
        if (max2 > total[k])
            max2 = total[k];
    }

    printf("%.2f", max2);

    return 0;
}