#include<bits/stdc++.h>
using namespace std;
double a[101];
int main(){
    double n,m,maxn=0,minn=99999,maxx=-1,sum=0;
    cin>>n>>m;
    for (int i=1;i<=n;i++){
        for (int j=1;j<=m;j++) {
            cin>>a[i];
            maxn=max(maxn,a[i]);
            minn=min(minn,a[i]);
            sum+=a[i];
        }
        sum-=maxn+minn;
        maxx=max(maxx,sum);
    }
    cout<<fixed<<setprecision(2)<<maxx/(m-2);
}