#include <bits/stdc++.h>

using namespace std;

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

int n, k, S;
int sl[1005][1005];
int sc[1005][1005];
int sd[1005][1005];

void Citire()
{
    int i, j, x;
    fin >> n >> k;
    for(i = 1; i <= n; i++)
        for(j = 1; j <= i; j++)
        {
            fin >> x;
            S += x;
            sl[i][j] = sl[i][j - 1] + x;
            sc[i][j] = sc[i - 1][j] + x;
            sd[i][j] = sd[i - 1][j - 1] + x;
        }
}

void Rezolva()
{
    int L, i, s, smin, s1, j;
    L = n - k;
    s = 0;
    for(i = 1; i <= L; i++)
        s += sl[i][i];
    smin = s1 = s;
    for(i = 2; i <= k + 1; i++)
    {
        s1 = s = s1 + sl[i + L - 1][L] - sd[i + L - 2][L];
        smin = min(smin, s);
        for(j = 2; j <= i; ++j)
        {
            s = s - (sc[i + L - 1][j - 1] - sc[i - 1][j - 1]) + (sd[i + L - 1][j + L - 1] - sd[i - 1][j - 1]);
            smin = min(smin, s);
        }
    }
    fout << S - smin << "\n";
}

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