#include <fstream>
using namespace std;

const int NMAX = 1001;

int N, K, a[NMAX][NMAX], sv[NMAX][NMAX], sh[NMAX][NMAX], sd[NMAX][NMAX];

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)
			fin>>a[i][j];
			
	int total = 0, ans = 0;
			
	for (int i=1;i<=N;++i)
		for (int j=1;j<=i;++j)
		{
			sh[i][j] = sh[i][j-1] + a[i][j];
			sv[i][j] = sv[i-1][j] + a[i][j];
			sd[i][j] = sd[i-1][j-1] + a[i][j];
			total += a[i][j];
		}
	
	//fprintf(stderr, "total: %d\n", total);
	
	int k = N - K;
	
	int current = 0;
	for (int i = 1;i<=k;++i)
		for (int j=1;j<=i;++j)
			current += a[i][j];
			
	//fprintf(stderr, "%d\n", current);
			
	ans = max(ans, total - current);
			
	for (int i = k+1;i <= N;++i)
	{
		current -= sd[i-1][k];
		current += sh[i][k];
		//fprintf(stderr, "%d\n", current);
		ans = max(ans, total - current);
		int copy = current;
		for (int j=2;j+k-1 <= i;++j)
		{
			current -= sv[i][j-1] - sv[i-k][j-1];
			current += sd[i][j+k-1] -sd[i-k][j-1];
			//fprintf(stderr, "%d\n", current);
			ans = max(ans, total - current);
		}
		current = copy;
	}
	
	fout<<ans<<"\n";
	
	return 0;
}