#include<stdio.h>

int main(){
    int M,N;
    scanf("%d %d", &M,&N);
    
    if(M <= 0 || N <= 0){
        printf("Invalid Input");
        return 0;
    }
    
    float a[105][105];
    float col[105];
    
    for (int i = 0; i < M ; i++){
        for(int j = 0; j < N; j++){
            scanf("%f", &a[i][j]);
            if(a[i][j] < 0){
                printf("Invalid Input");
                return 0;
            }
        }
        
        col[i] = a[i][0];   `                                       
    }
    
    for(int i=0;i < M-1;i++){
        for(int j=i+1; j < M; j++){
            if(col[i] > col[j]){
                float temp = col[i];
                col[i] = col[j];
                col[j] = temp;
            }
        }
    }
    
    float median;
    
    if(M % 2 == 1){
        median = col[M/2];
    }else{
        median = (col [M / 2 -1] + col[M / 2]) / 2.0;
    }
    
    printf("%.2f",median);
    
    
    return 0;
    
}