#include <cstdio>
#include <algorithm>

#define DIM 1024
#define INF 1000000000
using namespace std;

int N, K, matrix[DIM][DIM], line_sum[DIM][DIM], rectangle_sum[DIM][DIM], triangle_sum[DIM][DIM], minim, sum;

int main () {

    freopen ("ferma2.in" ,"r", stdin );
    freopen ("ferma2.out","w", stdout);

    scanf ("%d %d", &N, &K);
    for (int i = 1; i <= N; i ++)
        for (int j = 1; j <= i; j ++)
            scanf ("%d", &matrix[i][j]);

    for (int i = 1; i <= N; i ++)
    for (int j = 1; j <= N; j ++) {
        line_sum[i][j] = matrix[i][j] + line_sum[i][j-1];
        rectangle_sum[i][j] = rectangle_sum[i-1][j] + line_sum[i][j];
        triangle_sum[i][j] = triangle_sum[i-1][j-1] + line_sum[i][j];

        sum += matrix[i][j];
    }

    K = N - K; minim = INF;
    for (int i = K; i <= N; i ++)
        for (int j = K; j <= i; j ++)
            minim = min (minim, triangle_sum[i][j] - rectangle_sum[i][j-K] + rectangle_sum[i-K][j-K] - triangle_sum[i-K][j-K]);

    printf ("%d\n", sum - minim);

    return 0;
}