#include<fstream>
#include<vector>
#include<string>

using namespace std;

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


string sir;
int i, n, k, j,contor,st,dr,sol,x,y,sum,aux;
int a[1005][1005], col[1005][1005], diag[1005][1005];

int main()
{
    fin >> n >> k;
    k = n - k;
    sol = 2000000000;
    for(i = 1; i <= n; i++)
    {
        for(j = 1; j <= i; j++)
        {
            fin >> a[i][j];
            sum = sum + a[i][j];
            col[i][j] = col[i - 1][j] + a[i][j];
            diag[i][j] = diag[i - 1][j - 1] + a[i][j];
        }
    }
    for(i = k; i <= n; i++)
    {
        aux = 0; x = k;
        for(j = 1; j <= k; j++)
        {
            aux = aux + (col[i][j] - col[i - x][j]);
            x--;

        }
        sol = min(sol, aux);
        for(j = 2; j + k - 1 <= i; j++)
        {
            aux = aux - (col[i][j - 1] - col[i - k][j - 1]);
            aux = aux + (diag[i][j + k - 1] - diag[i - k][j - 1]);
            sol = min(sol, aux);

        }
    }
    fout << sum - sol <<"\n";
}