#include <iostream>
#include <fstream>
using namespace std;

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

int a[1005][1005], n, k, m;
int D[1005][1005];
int L[1005][1005];
int C[1005][1005];

int main()
{
    int i, j, s, s1, smin, st;
    fin >> n >> k;
    m = n - k;
    st = s = 0;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= i; j++)
        {
            fin >> a[i][j];
            st += a[i][j];
            if (i <= m) s += a[i][j];
            D[i][j] = a[i][j] + D[i - 1][j - 1];
            L[i][j] = a[i][j] + L[i][j - 1];
            C[i][j] = a[i][j] + C[i - 1][j];
        }

    smin = s;
    for (i = m + 1; i <= n; i++)
    {
        s -= D[i - 1][m];
        s += L[i][m];
        s1 = s;
        smin = min(smin, s);
        for (j = 2; j <= i - m + 1; j++)
        {
            s1 = s1 + D[i][j + m - 1] - D[i - m][j - 1];
            s1 = s1 - C[i][j - 1] + C[i - m][j - 1];
            smin = min(smin, s1);
        }
    }

    fout << st - smin << "\n";
    return 0;
}