#include <cstdio>
using namespace std;

const int NMAX = 1000;
int d[NMAX + 5][NMAX + 5];
int lin[NMAX + 5][NMAX + 5], col[NMAX + 5][NMAX + 5];
int main()
{
    freopen("ferma2.in", "r", stdin);
    freopen("ferma2.out", "w", stdout);

    int n, k, ans, x, st;
    scanf("%d %d", &n, &k);
    k = n - k;

    ans = 2000000000; st = 0;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= i; ++j)
        {
            scanf("%d", &x); st += x;
            lin[i][j] = lin[i][j - 1] + x;
            col[i][j] = col[i - 1][j] + x;
        }

    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= i; ++j)
        {
            d[i][j] = d[i - 1][j - 1] - (col[i - 1][j - k] - col[i - k - 1][j - k]);
            d[i][j] += (lin[i][j] - lin[i][j - k]);
            if (i >= k && j >= k && d[i][j] < ans)
                ans = d[i][j];
        }

    printf("%d\n", st - ans);
    return 0;
}