#include <bits/stdc++.h>
#define N 1005

using namespace std;

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

int mat[N][N] , lin[N][N] , col[N][N] , diag[N][N] , sump[N][N] ;

int main()
{
    int n , k , i , j , sum = 0 , kk , sumtr = 0 , trl = 0 , best = 0x3f3f3f3f ;
    fin >> n >> k ;
    kk = n-k;
    for ( i = 1 ; i <= n ; i++ )
    {
        for ( j = 1 ; j <= i ; j++ )
        {
            fin >> mat[i][j] ;
            sum += mat[i][j] ;
            col[i][j] = col[i-1][j] + mat[i][j] ;
            lin[i][j] = mat[i][j] + lin[i][j-1] ;
            diag[i][j] = diag[i-1][j-1] + mat[i][j] ;
            if ( j > kk )
                lin[i][j] = lin[i][j] - mat[i][j-kk] ;
            if ( i > kk )
                col[i][j] = col[i][j] - mat[i-kk][j] ;
            if ( i > kk && j > kk )
                diag[i][j] = diag[i][j] - mat[i-kk][j-kk] ;
        }
    }
    best = sum ;
    /*for ( i = 1 ; i <= n ; i++ )
    {
        for ( j = 1 ; j <= i ; j++ )
            cout << mat[i][j] << " " ;
        cout << endl ;
    }
    cout << endl ;*/
    /*for ( i = 1 ; i <= n ; i++ )
    {
        for ( j = 1 ; j <= i ; j++ )
            cout << lin[i][j] << " " ;
        cout << endl ;
    }
    cout << endl ;*/
    /*for ( i = 1 ; i <= n ; i++ )
    {
        for ( j = 1 ; j <= i ; j++ )
            cout << col[i][j] << " " ;
        cout << endl ;
    }
    cout << endl ;*/
    /*for ( i = 1 ; i <= n ; i++ )
    {
        for ( j = 1 ; j <= i ; j++ )
            cout << diag[i][j] << " " ;
        cout << endl ;
    }
    cout << endl ;*/
    for ( i = 1 ; i <= kk ; i++ )
        sumtr = sumtr + lin[i][i] ;
    //cout << sumtr << endl ;
    trl = sumtr;
    if ( sumtr < best )
        best = sumtr ;
    for ( i = 2 ; i <= k+1 ; i++ )
    {
        sumtr = trl - diag[i+kk-2][kk] + lin[i+kk-1][kk] ;
        trl = sumtr ;
        //cout << " pt i " << i << " " << sumtr << endl ;
        for ( j = 1 ; j < i ; j++ )
        {
            //cout << " pt j " << j << " " ;
            if ( sumtr < best )
                best = sumtr ;
            sumtr = sumtr - col[i+kk-1][j] + diag[i+kk-1][j+kk] ;
            //cout << sumtr << endl ;
        }
        if ( sumtr < best )
            best = sumtr ;
    }
    //cout << best << " " << sum << endl ;
    fout << sum-best ;
}