#include <bits/stdc++.h>

using namespace std;


/**

    82
    55 3
    67 46 52
    62 20 54 85
    66 32 40 78 52


    1.facem sume partiale pe linii, coloane, diagonale
    2.determinam subtriunghuil de latura L = n - k de suma minima
*/


int a[1002][1002];

int stot;

int n, k;
/// sume partiale pe linii, coloane, diagonale
int sc[1002][1002];
int sl[1002][1002];
int sd[1002][1002];

ofstream fout("ferma2.out");

void Read()
{
    ifstream fin("ferma2.in");
    fin >> n >> k;

    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= i; j++)
        {
            fin >> a[i][j];
            stot += a[i][j];
        }
    fin.close();
}

void Sume_Partiale()
{
    int i, j;

    for (i = 1; i <= n; i++)
        for (j = 1; j <= i; j++)
        {
            sl[i][j] = sl[i][j - 1] + a[i][j];
            sc[i][j] = sc[i - 1][j] + a[i][j];
            sd[i][j] = sd[i - 1][j - 1] + a[i][j];
        }
}

void Solve()
{
    int i, j, s(0);
    int smin, suma;
    int L = n - k; /// lg subtringhiului


    /// Suma primului subtriunghi cu coltul in (1, 1)
    for (i = 1; i <= L; i++)
            s += sl[i][i];
    smin = suma = s;

    for (i = L + 1; i <= n; i++)
    {
        s = s - sd[i - 1][L] + sl[i][L];
        suma = s;
        smin = min(smin, suma);
        for (j = L + 1; j <= i; j++)
        {
            suma = suma - (sd[i][j] - sd[i - L][j - L]) + sl[i][j] - sl[i][j - L];
            smin = min(smin, suma);
        }
    }

    fout << (stot - smin) << "\n";
}

int main()
{
    Read();
    Sume_Partiale();
    Solve();
    return 0;
}