#include<bits/stdc++.h>
using namespace std;
int s[25],n,m,maxsum;
void stat(int a[],int m){
    int maxscore = 0,minscore = 10,sum = 0;
    for(int i=0;i<m;i++){
        maxscore = max(a[i],maxscore);
        minscore = min(a[i],minscore);
        sum += a[i];
    }
    maxsum = max(maxsum,sum-maxscore-minscore);
}
int main(){
    cin>>n>>m;
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            cin>>s[j];
        }
        stat(s,m);
    }
    printf("%.2f",double(maxsum)/(m/2));
    return 0;
}