#include<iostream>
#include<fstream>
using namespace std;
int a[1001][1001],sum,s_crt,t,mini=1000000;
int  n,k,i,j;
int main(void)
{

	ifstream f("ferma2.in");
	ofstream g("ferma2.out");
	f>>n>>k;
	for (i=1;i<=n;i++)
		for (j=1;j<=i;j++)
		{
			
			f>>a[i][j];
			sum+=a[i][j];
			a[i][j]=a[i][j]+a[i-1][j-1];
	
		}
	int m=n-k;
	for (i=n;i>=m;i--)
		for (j=i;j>=m;j--)
		{
			
			s_crt=0;
			s_crt=a[i][j];
			for (t=i-m;t<i;t++)
			{
				
				s_crt=s_crt-a[t][j-m];
				
			}
			for (t=j-1;t>j-m;t--)
				s_crt=s_crt+a[i][t];
			
			if (s_crt<mini)
				mini=s_crt;
	
		}
	g<<sum-mini;
}