#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);
}