#include<stdio.h>
#include<stdlib.h>
int compare_floats(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),compare_floats);
    float median;
    if(m%2==1){
        median=price[m/2];
    }
    else{
        median=price[m/2-1]+prices[m/2])/2.0;
    }
    printf("%.2f\n",median);
    return 0;
}