#include <bits/stdc++.h>

using namespace std;
ifstream fin("ferma2.in");
ofstream fout("ferma2.out");
int n, k, v[1003][1003], sp[1003][1003]; ///sp[i][j] = v[i][1] + ... + v[i][j]
int sumTotal;

int main()
{
    fin >> n >> k;
    for(int i=1; i<=n; i++) {
        for(int j=1; j<=i; j++) {
            fin >> v[i][j];
            sp[i][j] = sp[i][j - 1] + v[i][j];
            sumTotal += v[i][j];
        }
    }
    int lat = n - k, minim = 2e9;
    for(int i=1; i+lat-1<=n; i++) {
        for(int j=1; j<=i && j+lat-1<=n; j++) {
            int curent = 0;
            for(int l=1; l<=lat; l++) curent += sp[i + l - 1][j + l - 1] - sp[i + l - 1][j - 1];
            minim = min(minim, curent);
        }
    }
    fout << sumTotal - minim;

    return 0;
}