#include <bits/stdc++.h>

using namespace std;
/**
    facem sume partiale pe linii,coloane,diagonale
    determinam subtriunghiul de latura L=n-k
    de suma minima
*/
const short NMAX=1001;
int lin[NMAX][NMAX],col[NMAX][NMAX],diag[NMAX][NMAX],lat;
int n,k,a[NMAX][NMAX],Stotal;
ifstream fin("ferma2.in");
ofstream fout("ferma2.out");
inline void READ()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=i;j++)
        {
            fin>>a[i][j];
            int x=a[i][j];
            Stotal+=x;
        }
}
inline void SUM_Part()
{
    for(int i=1;i<=n;i++)
        for(int j=1;j<=i;j++)
    {
        lin[i][j]=lin[i][j-1]+a[i][j];
        col[i][j]=col[i-1][j]+a[i][j];
        diag[i][j]=diag[i-1][j-1]+a[i][j];
    }
}
inline void DP()
{
    lat=n-k;
    int s,smin,suma;
    ///calculez suma formata din primele lat linii
    smin=0;
    for(int i=1;i<=lat;i++)
        smin+=lin[i][i];
    suma=s=smin;
    for(int i=lat+1;i<=n;i++)
    {
        s-=(diag[i-1][lat] + lin[i][lat]);
        suma=s;
        smin=min(smin,s);
        for(int j=lat+1;j<=i;j++)
        {
            suma=suma-(diag[i][j]-diag[i-lat][j-lat])+(col[i][j-lat]-col[i-lat][j-lat]);
            smin=min(smin,suma);
        }
    }
    fout<<(Stotal-smin)<<"\n";
}
int main()
{
    READ();
    SUM_Part();
    DP();
    fin.close();
    fout.close();
    return 0;
}