#include<fstream>
#define INF 1001
using namespace std;
long i,j,n,t;
long S1[INF][INF],S2[INF][INF],S3[INF][INF];
long n2,s,sact,minim=INF*INF,rez;
long T[INF][INF];
int main()
{
    ifstream in("ferma2.in");
    ofstream out("ferma2.out");
    in>>n;
    in>>t;
    for ( i=1; i<=n; ++i)
        for ( j=1; j<=i; ++j)
            in>>T[i][j];
    for ( i=1; i<=n; ++i)
        for ( j=1; j<=i; ++j)
            S1[i][j]=S1[i][j-1]+T[i][j];
    for ( i=1; i<=n; ++i)
        for ( j=1; j<=i; ++j)
            S2[i][j]=S2[i-1][j-1]+T[i][j];
    for ( i=1; i<=n; ++i)
        for ( j=1; j<=i; ++j)
            S3[i][j]=S3[i-1][j]+T[i][j];
    n2=n-t;
    // calculam suma initiala, aceasta fiind suma patratului avand coltul in n2.n2;
    for ( i=1; i<=n2; ++i)
        s+=S1[i][i];
    for ( i=1; i<=n; ++i)
        rez+=S1[i][i];
    // S1 .. suma le linie
    // S2 .. suma pe diagonala
    // S3 .. suma pe coloana
    sact=s;
/*    for ( i=1; i<=n; ++i,out<<"\n")
        for ( j=1; j<=i; ++j)
            out<<T[i][j]<<" ";
     out<<"\n\n\n";
*/
   /* for ( i=1; i<=n; ++i,out<<"\n")
        for ( j=1; j<=i; ++j)
            out<<S1[i][j]<<" ";
     out<<"\n\n\n";

    for ( i=1; i<=n; ++i,out<<"\n")
        for ( j=1; j<=i; ++j)
            out<<S2[i][j]<<" ";
     out<<"\n\n\n";

    for ( i=1; i<=n; ++i,out<<"\n")
        for ( j=1; j<=i; ++j)
            out<<S3[i][j]<<" ";*/

    for ( i=n2; i<=n; ++i)
    {
        s=sact;
  //      out<<i<<" "<<n2<<" "<<s<<"\n";
        if ( s < minim)
            minim=s;
        for ( j=n2; j<=i-1; ++j)
        {
            //out<<"\n\n\n\n";
            s+=S2[i][j+1];
            //out<<i<<" "<<j+1<<" "<<s<<"\n";
            s-=S2[i-n2][j-n2+1];
            //out<<i<<" "<<j+1<<" "<<s<<"\n";
            s-=S3[i][j-n2+1];
            //out<<i<<" "<<j+1<<" "<<s<<"\n";
            s+=S3[i-n2][j-n2+1];
    //        out<<i<<" "<<j+1<<" "<<s<<"\n";
            if ( s<minim )
                minim=s;
        }

        sact+=S1[i+1][n2+1];
        sact-=S2[i+1][n2+1];
        //sact+=T[i+1][n2+1];
    }
    out<<rez-minim;

    return 0;
}