#include <fstream>
using namespace std;

ifstream fin("ferma2.in");
ofstream fout("ferma2.out");

int a[1002][1002];
int L[1002][1002];
int C[1002][1002];
int D[1002][1002];
int n, k, m;

int main()
{
    int i, j;
    int s, smin, s1, total = 0;
    fin >> n >> k;
    m = n - k;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= i; j++)
        {
            fin >> a[i][j];
            total += a[i][j];
            L[i][j] = L[i][j - 1] + a[i][j];
            C[i][j] = C[i - 1][j] + a[i][j];
            D[i][j] = D[i - 1][j - 1] + a[i][j];
        }
    s = 0;
    for (i = 1; i <= m; i++)
        s += L[i][i];
    s1 = smin = s;
    for (i = m + 1; i <= n; i++)
    {
        s = s1 = s1 + L[i][m] - D[i - 1][m];
        smin = min(smin, s);
        for (j = m + 1; j <= i; j++)
        {
            s = s - (C[i][j - m] - C[i - m][j - m]) +
                (D[i][j] - D[i - m][j - m]);
            smin = min(smin, s);
        }
    }
    s = total - smin;
    fout << s << "\n";
    fout.close();
    return 0;
}