#include <stdio.h>
#define LEN 1005

int M[LEN][LEN];
int n, k;

int 
main(void)
{
    int i, j;
    int coloana, linie;
    int s1, s2, s3, S;
    
    freopen("ferma2.in", "r", stdin);
    freopen("ferma2.out", "w", stdout);
    
    scanf("%d %d", &n, &k);
    
    for(i = 0; i < n; i++)
    	for(j = 0; j <= i; j++)
    	      scanf("%d", &M[i][j]);
    
    S = coloana = linie = 0;
    
    while(k > 0 && k < n)
    {
            s1 = s2 = s3 = 0;
            for(i = linie; i <= n; i++)
                  s1 += M[i][coloana];
            for(i = coloana; i <= n; i++)
                  s2 += M[n - 1][i];
            for(i = 0; i <= n; i++)
                  s3 += M[linie + i][coloana + i];           
            
            if(s1 >= s2 && s1 >= s3)
                 S += s1, coloana++, linie++;
            else if(s2 >= s1 && s2 >= s3)
                 S += s2;
            else if(s3 >= s1 && s3 >= s2)
                 S += s3, linie++;
            
            n--;
            k--;
    }
    
    printf("%d", S);
    return 0;
}