#include<stdio.h>
#include<stdio.h>
int com(const void*a,const void *b)
{
    float fa=*(const float*)a;
    float fb=*(const float*)b;
    return (fa>fb)-(fa<fb);
}
int main()
{
    int m,n;
    if(scanf("%d %d",&m,&n)!=2||m<=0||n<=0)
    {
        printf("Invalid Input");
        return 0;
    }
    float prices[m];
    for(int i=0;i<m;i++)
    {
        for(int j=0;j<n;j++)
        {
          float price;
          if(scanf("%f",&price)!=1||price<0)
          {
              printf("Invalid Input");
              return 0;
          }
          if(j==0)
          {
              prices[i]=price;
          }
        }
    }
    qsort(prices,m,sizeof(float),com);
    float median;
    if(n%2==1)
    {
        median=prices[m/2];
    }
    else
    {
        median=(prices[m/2-1]-price[m/2])/2.0;
    }
    printf("%.2f\n",median);
    return 0;
}