#include <bits/stdc++.h>

using namespace std;
ifstream f("ferma2.in");
ofstream g("ferma2.out");
int s,Min,s1,sum=0,n,m,k,a[1005][1005],mat1[1005][1005],mat2[1005][1005],mat3[1005][1005];
int main()
{
    f>>n>>k;
    m=n-k;
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=i; j++)
        {
            f>>a[i][j];
            sum+=a[i][j];
            mat1[i][j]=mat1[i][j-1]+a[i][j];
            mat2[i][j]=mat2[i-1][j]+a[i][j];
            mat3[i][j]=mat3[i-1][j-1]+a[i][j];
        }
    }
    s=0;
    for(int i=1; i<=m; i++)
    {
        s+=mat1[i][i];
    }
    s1=Min=s;
    for(int i=m+1; i<=n; i++)
    {
        s=s1=s1+mat1[i][m]-mat3[i-1][m];
        Min=min(Min,s);
        for(int j=m+1; j<=i; j++)
        {
            s=s-(mat2[i][j-m]-mat2[i-m][j-m])+(mat3[i][j]-mat3[i-m][j-m]);
            Min=min(Min,s);
        }
    }
    g<<sum-Min<<"\n";
    return 0;
}