#include <fstream>

using namespace std;

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

/// facem sume partiale pe linii, coloane, diagolanle
/// determinam subtriunghiul de latura L = n-k (dupa k zile) de suma minima, restul ramas va fi suma maxima cautata

int sl[1005][1005], sc[1005][1005], sd[1005][1005]; /// sume partiale pe linii, coloane, diagonale
int S, smin; /// S - suma totala

int main()
{
    int n, k;
    fin >> n >> k;
    int L = n-k;

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

    for(int i = 1; i <= L; ++i)
        smin += sl[i][i];
    int suma, s; /// s - triunghiul lipit de cateta stanga
    suma = s = smin;
    for(int i = L + 1; i <= n; ++i)
    {
        s = s - sd[i-1][L] + sl[i][L];
        suma = s;
        smin = min(smin, suma);
        for(int j = L+1; j <= i; ++j)
        {
            suma = suma - (sd[i][j] - sd[i-k][j-k]) + (sc[i][j-k] - sc[i-k][j-k]);
            smin = min(smin, suma);
        }
    }
    fout << S - smin;
    return 0;
}

/*
56
82 5
55 3 11
67 46 52 12
62 20 54 85 14
66 32 40 78 52 22
*/