#include <bits/stdc++.h>

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

int a[1005][1005];
int L[1005][1005];
int C[1005][1005];
int D[1005][1005];
int n,m,k;

int main()
{
    int i,j;
    int s,smin,s1,total=0;
    fin >> n >> k;
    m=n-k;
    for (i=1; i<=n; i++)
    for (j=1; j<=i; j++)
    {
        fin >> a[i][j];
        total+=a[i][j];
        L[i][j]=L[i][j-1]+a[i][j];
        C[i][j]=C[i-1][j]+a[i][j];
        D[i][j]=D[i-1][j-1]+a[i][j];
    }
    s=0;
    for (i=1; i<=m; i++)
        s+=L[i][i];
    s1=smin=s;
    for (i=m+1; i<=n; i++)
    {
        s=s1=s1+L[i][m]-D[i-1][m];
        smin=min(smin,s);
        for (j=m+1; j<=i; j++)
        {
            s=s-C[i][j-m]+C[i-m][j-m]+D[i][j]-D[i-m][j-m];
            smin=min(smin,s);
        }
    }
    fout << total-smin;

    return 0;
}