#include<iostream>
#include<fstream>
using namespace std;
long long  a[1008][1008],sum,s_crt,t,mini=101000000;
int main(void)
{
	int  n,k,i,j,w;
	FILE *f=fopen("ferma2.in","r");
fstream g("ferma2.out",ios::out);
	fscanf(f,"%d%d",&n,&k);
	for (i=1;i<=n;i++)
		for (j=1;j<=i;j++)
		{
			
			fscanf(f,"%d",&w);
			a[i][j]=w;
			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;
			int r=m;
			for(t=j;t>j-m;t--)
			{
				s_crt+=(a[i][t]-a[i-r][t-r]);
				r--;
			}
			
			if (s_crt<mini)
				mini=s_crt;
	
		}
	g<<sum-mini;
}