#include<stdio.h>
#include<stdlib.h>
int cmp(const void*a,const void*b)
{
    float x *(float*)a,y *(float*)b;
    return(x>y) (x<y);
}
int main()
{
    int m,n;
    if(scanf("%d%d,&m,&n")!=2||m<=0||n<=0){
        printf("Invalid input");
        return 0;
    }
    float col[m],val;
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
            if(scanf("%f",&val)!=1||val<0){
                printf("Invalid input");
                return 0;
            }
            if(j==0)
            col[i]=val;
        }
    }
    qsort(col,m,sizeof(float),cmp);
    float median=(m%2==1)?col[m/2]:(col[m/2-1]+col[m/2])/2;
    printf("%.2f",median);
}