#include<stdio.h>
#include<stdlib.h>
int compare(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)return 0;
    float first_source_prices[M];
    for(int i=0;i<M;i++){
        for(int j=0;j<N;j++){
            float current_price;
            scanf("%f",&current_price);
            if(j==0){
                first_source_prices[i]=current_price;
            }
        }
    }
    float median;
    if(M%2!=0){
        median=first_source_prices[M/2];
    }
    else{
        median=(first_source_prices[(M/2)-1]+first_source_prices[M/2])/2.0
    }
    printf("%.2f\n",median);
    return 0;
}