#include <bits/stdc++.h>
#define Nmax 1005

using namespace std;

int n, k, S;
int sl[Nmax][Nmax];
int sc[Nmax][Nmax];
int sd[Nmax][Nmax];

void Citire()
{
    ifstream f("ferma2.in");
    f >> n >> k;
    int i, j, pret;
    for(i = 1; i <= n; i++)
        for(j = 1; j <= i; j++)
        {
           f >> pret;
           S += pret;
           sl[i][j] = sl[i][j - 1] + pret;
           sc[i][j] = sc[i - 1][j] + pret;
           sd[i][j] = sd[i - 1][j - 1] + pret;
        }
    f.close();
}

void Rezolv()
{
    int lat, i, j, sum, s1, smin;
    lat = n - k;
    sum = 0;
    for(i = 1; i <= lat; i++)
        sum += sl[i][i];
    smin = s1 = sum;
    for(i = 2; i <= k + 1; i++)
    {
        s1 = sum = s1 + sl[i + lat - 1][lat] - sd[i + lat - 2][lat];
        smin = min(smin, sum);
        for(j = 2; j <= i; j++)
        {
            sum = sum - (sc[i + lat - 1][j - 1] - sc[i - 1][j - 1]) +
                         (sd[i + lat - 1][j + lat - 1] - sd[i - 1][j - 1]);
            smin = min(smin, sum);
        }
    }
    ofstream g("ferma2.out");
    g << S - smin << "\n";
    g.close();
}

int main()
{
    Citire();
    Rezolv();
    return 0;
}