#include <fstream>

using namespace std;

ifstream cin("ferma2.in");
ofstream cout("ferma2.out");

const int INF = 1000000000;
const int MAXN = 1000;

int leftSum[1 + MAXN][1 + MAXN], downSum[1 + MAXN][1 + MAXN], diagonalSum[1 + MAXN][1 + MAXN];

int main() {
    int n, k, sum = 0, best = INF;
    cin >> n >> k;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= i; j++) {
            int x;
            cin >> x;
            sum += x;
            leftSum[i][j] = leftSum[i][j - 1] + x;
            downSum[i][j] = downSum[i - 1][j] + leftSum[i][j];
            diagonalSum[i][j] = diagonalSum[i - 1][j - 1] + leftSum[i][j];
        }
    k = n - k;
    for (int i = k; i <= n; i++)
        for (int j = k; j <= i; j++)
            best = min(best, diagonalSum[i][j] - downSum[i][j - k] + downSum[i - k][j - k] - diagonalSum[i - k][j - k]);
    cout << sum - best;
    return 0;
}