#include <bits/stdc++.h>

using namespace std;

int n,k,sum,ans,linie[1009][1009],col[1009][1009],diag[1009][1009],din[1009][1009];

int main()
{
    ifstream fin("ferma2.in");
    ofstream fout("ferma2.out");
    fin>>n>>k;
    for(int i=1; i<=n; ++i)
    {
        for(int j=1; j<=i; ++j)
        {
            int x;
            fin>>x;
            sum+=x;
            linie[i][j]=linie[i][j-1]+x;
            col[i][j]=col[i-1][j]+x;
            diag[i][j]=diag[i-1][j-1]+x;
        }
    }
    int m=n-k;
    for(int i=1; i<=m; ++i)
    {
        din[1][1]+=linie[i][i];
    }
    ans=din[1][1];
    for(int i=2; i+m-1<=n; ++i)
    {
        din[i][1]=din[i-1][1]-diag[i+m-2][m]+linie[i+m-1][m];
        ans=min(ans,din[i][1]);
        for(int j=2; j<=i; ++j)
        {
            din[i][j]=din[i][j-1]-col[i+m-1][j-1]+col[i-1][j-1]+diag[i+m-1][j+m-1]-diag[i-1][j-1];
            ans=min(ans,din[i][j]);
        }
    }
    fout<<sum-ans<<"\n";
    return 0;
}