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

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

int n, m, k;
int a[1005][1005];
int C[1005][1005];
int L[1005][1005];
int D[1005][1005];


int main()
{
    int i, j, Total, S, S1, sMin;
    fin >> n >> k;

    Total = S = 0;
    m = n - k;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= i; j++)
        {
            fin >> a[i][j];
            Total += a[i][j];
            if (i <= m)
                S += a[i][j];
            C[i][j] = a[i][j] + C[i - 1][j];
            L[i][j] = a[i][j] + L[i][j - 1];
            D[i][j] = a[i][j] + D[i - 1][j - 1];
        }
    sMin = S;
    for (i = m + 1; i <= n; i++)
    {
        S = S - D[i - 1][m] + L[i][m];
        S1 = S;
        sMin = min(sMin, S);
        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 << Total - sMin << "\n";
    return 0;
}