#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>

double average (int size)
{
    std::vector<int> scores (size);
    for(int i = 0; i<size; i++)
    {
        std::cin>>scores[i];
    }
    std::sort(scores.begin(),scores.end());
    int sum = 0;
    for (int i = 1;i<size-1;i++)
    {
        sum += scores[i];
    }
    double ave = sum / (size-2);
    return ave;
}

//P5738
int main(void)
{
    int student_num;
    int size;
    std::cin>>student_num>>size;
    if (size>2)
    {
        std::vector<double> student_ave_scores(student_num);
        for (int i = 0 ; i < student_num ; i++)
        {
            student_ave_scores[i] = average(size);
        }
        std::sort(student_ave_scores.begin(),student_ave_scores.end());
        std::cout<<std::fixed<<std::setprecision(2)<<student_ave_scores[student_num-1]<<std::endl;
    }
    else
    {
        std::cout<<"";
    }
}