#include <iostream>
#include <cstdio>
using namespace std;
int m,n,big=0;
double score(){
    int a[100000]={0},maxs=0,mins=10;double scores=0,sum=0;
    for(int i=0;i<m;i++){
        cin>>a[i];
        if(a[i]>=maxs)maxs=a[i];
        if(a[i]<mins)mins=a[i];
        sum+=a[i];
    }
    sum=sum-maxs-mins;
    scores=sum/(m-2);
    return scores;
}
int main(){
int arr[100000];
cin>>n>>m;
    for(int i=0;i<n;i++){
        arr[i]=score();
    }
    for(int i=0;i<n;i++){
        if(arr[i]>big)big=arr[i];
    }
    printf("%.2f",double (big));
    return 0;
}