#include <bits/stdc++.h>
using namespace std;

/**
infoarena.ro/cauta-probleme

Triunghium cu m linii si m coloane
cu suma minima

5 3
82
55 3
67 46 52
62 20 54 85
66 32 40 78 52
*/
ifstream fin("ferma2.in");
ofstream fout("ferma2.out");
int a[1005][1005], n, k, m;
int L[1005][1005];
int C[1005][1005];
int D[1005][1005];
int smin, s, s1, ST;

int main()
{
    int i, j;
    fin >> n >> k;
    m = n - k;
    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];
            L[i][j] = a[i][j] + L[i][j-1];
            C[i][j] = a[i][j] + C[i-1][j];
            D[i][j] = a[i][j] + D[i-1][j-1];
        }
    smin = s;
    for (i = m+1; i <= n; i++)
    {
        s1 = s = s - D[i-1][m] + L[i][m];
        smin = min(smin, s1);
        for (j = 2; j <= i-m+1; j++)
        {
            s1 = s1 - (C[i][j-1]-C[i-m][j-1])
             + D[i][j+m-1] - D[i-m][j-1];
            smin = min(smin, s1);
        }
    }
    fout << ST - smin;
    return 0;
}