#include <bits/stdc++.h>
using namespace std;
int main(){
    int n,m;
    cin >> n >> m;
    int a[n][m];
    double score[n]={0};
    for(int i=0;i<=n-1;i++){
        for(int j=0;j<=m-1;j++){
            cin >> a[i][j];
        }
        sort(a[i],a[i]+m);
    }
    for(int i=0;i<=n-1;i++){
        for(int j=1;j<=m-2;j++){
            score[i]+=a[i][j];
        }
        score[i]/=m-2;
    }
    sort(score,score+n);
    cout<<fixed<<setprecision(2)<<score[m-1];
}