#include<cstdio>
using namespace std;
int v[1001][1001],w[1001][1001];
int main()
{
	freopen("ferma2.in","r",stdin);
	freopen("ferma2.out","w",stdout);
	int n,k,i,j,max=0,r,nr,min;
	scanf("%d%d",&n,&k);
	k=n-k;
	for(i=1;i<=n;i++)for(j=1;j<=i;j++)
	{
		scanf("%d",&v[i][j]);
		max+=v[i][j];
		min=max;
		w[i][j]=w[i-1][j]+v[i][j];
	}
	for(i=k;i<=n;i++)
		for(j=1;j<=i-k+1;j++)
		{
			nr=0;
			for(r=1;r<=k;r++)nr=nr+w[i][r+j-1]-w[i-k+r-1][r+j-1];
			if(nr<min)min=nr;
		}
	max=max-min;
	printf("%d",max);
	return 0;
}