#include <fstream>
using namespace std;
ifstream cin("ferma2.in");
ofstream cout("ferma2.out");
struct chestii{
    int l,c,d;
};
chestii nr[1002][1002];
int main()
{
    int sump=0,sumi=0,a,sum=0,n,k,i,j,min1;
    cin>>n>>k;
    for(i=1;i<=n;i++)
        for(j=1;j<=i;j++)
        {
            cin>>a;
            sum+=a;
            nr[i][j].l=nr[i][j-1].l+a;
            nr[i][j].c=nr[i-1][j].c+a;
            nr[i][j].d=nr[i-1][j-1].d+a;
        }
    k=n-k;
    for(i=1;i<=k;i++)
        sumi+=nr[i][i].l;
    min1=sumi;
    for(i=2;i<=n-k+1;i++)
    {
        sumi+=nr[i+k-1][k].l;
        sumi-=nr[i+k-2][k].d;
        min1=min(sumi,min1);
        sump=sumi;
        for(j=2;j<=i;j++)
        {
            sump=sump+nr[i+k-1][j+k-1].d-nr[i-1][j-1].d;
            sump=sump-nr[i+k-1][j-1].c+nr[i-1][j-1].c;
            min1=min(sump,min1);
        }
    }
    cout<<sum-min1;
    return 0;
}