#include<stdio.h>
int main()
{
    int m,n,i,j,a[101][21]={0},max=0,min=10,sum=0;
    double max1=0,f;
    scanf("%d %d\n",&n,&m);
    for(i=0;i<n;i++){
        for(j=0;j<m;j++){
            scanf("%d",&a[i][j]);
            sum+=a[i][j];
            if(a[i][j]>max)
            max=a[i][j];
            if(a[i][j]<min)
            min=a[i][j];
        }
        f=(sum-max-min)/(m-2.0);
        if(f>max1)
        max1=f;
    }
    printf("%.2lf",max1);
    return 0;
    
    
}