#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("ferma2.in");
ofstream fout("ferma2.out");

int v[1003][1003], s[1003][1003], c[1003][1003], l[1003][1003], d[1003][1003];
int n, k, j, i, sum, mn, sM;

int main () {
	
	fin >> n >> k;
	k = n-k;
	for (i = 1; i <= n; i++)
		for (j = 1; j <= i; j++)
		{
			fin >> v[i][j];
			c[i][j] = v[i][j];
			d[i][j] = v[i][j];
			l[i][j] = v[i][j];
		}
	
	for (i = 1; i <= n; i++)
		for (j = 1; j <= i; j++)
		{
			l[i][j] += l[i][j-1];
			c[i][j] += c[i-1][j];
			d[i][j] += d[i-1][j-1];
			if (i <= k)	sum += v[i][j];
			sM += v[i][j];
		}
	s[k][k] = sum;
	
	mn = sM;
	for (i = 1; i <= n; i++)
		for (j = 1; j <= i; j++)
		{
			if (s[i-1][j] != 0)
			{
				s[i][j] += s[i-1][j];
				s[i][j] += l[i][j]-l[i][j-k];
				s[i][j] -= d[i-1][j]-d[i-k-1][j-k];
			}
			else if (s[i][j-1] != 0)
			{
				s[i][j] += s[i][j-1];
				s[i][j] += d[i][j]-d[i-k][j-k];
				s[i][j] -= c[i][j-k]-c[i-k][j-k];
			}
			if (j >= k && i >= k && s[i][j] < mn)	mn = s[i][j];
		}
	
	fout << sM-mn << "\n";
}