#include <fstream>
#include <vector>
#include <algorithm>
#include <cstring>

const int kMaxDim = 1005;

int a[kMaxDim][kMaxDim];
int sumLine[kMaxDim][kMaxDim], sumColumn[kMaxDim][kMaxDim], sumDiagonal[kMaxDim][kMaxDim];

int main() {
	std::ifstream inputFile("ferma2.in");
	std::ofstream outputFile("ferma2.out");

	int n, k;
	inputFile >> n >> k;

	int totalSum = 0;
	for (int i = 1; i <= n; ++i)
		for (int j = 1; j <= i; ++j) {
			inputFile >> a[i][j];

			totalSum += a[i][j];
			sumLine[i][j] = a[i][j] + sumLine[i][j - 1];
			sumColumn[i][j] = a[i][j] + sumColumn[i - 1][j];
			sumDiagonal[i][j] = a[i][j] + sumDiagonal[i - 1][j - 1];
		}

	int size = n - k;

	if (size == 0) {
		outputFile << totalSum << '\n';
		return 0;
	}

	int minSum = 0;
	for (int i = 1; i <= size; ++i)
		minSum += sumLine[i][i];

	int startSum = minSum;
	for (int i = 2; i + size - 1 <= n; ++i) {
		startSum += sumLine[i + size - 1][size];
		startSum -= sumDiagonal[i - 1 + size - 1][1 + size - 1];

		int currSum = startSum;
		minSum = std::min(minSum, currSum);

		for (int j = 2; j <= i; ++j) {
			currSum += sumDiagonal[i + size - 1][j + size - 1] - sumDiagonal[i - 1][j - 1];
			currSum -= sumColumn[i + size - 1][j - 1] - sumColumn[i - 1][j - 1];

			minSum = std::min(minSum, currSum);
		}
	}

	outputFile << totalSum - minSum << '\n';

	inputFile.close();
	outputFile.close();

	return 0;
}

//Trust me, I'm the Doctor!