#include＜bius/std++. h
using namespace std;
int main(){
   int a[101][21],n,m,maxx,minn;
   cin>>n>>m;
   for(int i=1;i<=n,i++){
       maxx=-1;minn=11;
       for(int j=1;j<=m;j++){
            cin>>a[i][j];
            if(maxx<a[i][j])
                maxx=a[i][j];
            if(minn>a[i][j])
                minn=a[i][j];
            a[i][0]+=a[i][j];
       }
       a[i][0]-=maxx+minn;
   }
   maxx=0;
   for(int i=1;i<=n;i++){
        if(maxx<a[i][0])
            maxx=a[i][0];
   }
   cout<<fixed<<setprecision(2)<<double(maxx/2)<<endl;
   return 0;
}