#include <fstream>
using namespace std;
ifstream fin ("ferma2.in");
ofstream fout ("ferma2.out");
struct ura
{
    int l,c,d;
};
ura sp[1001][1001];
int main ()
{
    int st=0,s=0,n,k,i,j,x,mini,cs;
    fin>>n>>k;
    k=n-k;
    for (i=1;i<=n;i++)
        for (j=1;j<=i;j++)
        {
            fin>>x;
            st+=x;
            sp[i][j].l=sp[i][j-1].l+x;
            sp[j][i].c=sp[j][i-1].c+x;
            sp[i][j].d=sp[i-1][j-1].d+x;
        }
    for (i=1;i<=k;i++)
        s+=sp[i][i].l;
    mini=s;
    for (i=2;i<=n-k+1;i++)
    {
        s+=sp[i+k-1][k].l;
        s-=sp[i+k-2][k].d;
        cs=s;
        if (cs<mini)
            mini=cs;
        for (j=2;j<=i;j++)
        {
            cs=cs+sp[i+k-1][j+k-1].d-sp[i-1][j-1].d;
            cs=cs-sp[j-1][i+k-1].c+sp[j-1][i-1].c;
            if (cs<mini)
                mini=cs;
        }
    }
    fout<<st-mini;
    return 0;
}