#include <bits/stdc++.h>
#define nmax 1001
using namespace std;

int sl[nmax][nmax], sc[nmax][nmax], sd[nmax][nmax], n, k, L, S;

int main()
{
    int i, j, x, s, s1, smin;
    ifstream fin("ferma2.in");

    fin >> n >> k;

    L = n - k;

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

    s = 0;
    for (i = 1; i <= L; ++i)
        s += sl[i][i];

    smin = s1 = s;

    for (i = 2; i <= n - L + 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);
        }
    }
    ofstream fout("ferma2.out");

    smin = S - smin;

    fout << smin << "\n";

    return 0;
}