#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[M][N], c[M];
    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;
            }
        }
        c[i] = a[i][0];
    }
    
    for (int i = 0; i < M - 1; i++)
         for (int j = i + 1; j < M; j++)
             if (c[i] > c[j]) {
                 float t = c[i]; c[i] = c[j];
             }
             
    float m = (M % 2) ? c[M / 2] : (c[M / 2 - 1] + c[M / 2] / 2;
    printf("%.2f", m);
    
    return 0;
}