#include<cstdio>
const int INF=100000005;
int a[1001][1001];
int n,k,smin,s,n2;

void read()
{
	int i,j;
	freopen("ferma2.in","r",stdin);
	freopen("ferma2.out","w",stdout);
	scanf("%d%d",&n,&k);
	s=0;
	for(i=1;i<=n;++i)
		for(j=1;j<=i;++j)
		{
			scanf("%d",&a[i][j]);
			s+=a[i][j];
			a[i][j]+=a[i-1][j-1];
		}
}

void work()
{
	int i,j,l;
	smin=INF; n2=n-k;
	for(i=n2;i<=n;++i)
		for(j=i;j>=n2;--j)
		{
			int sx=0;
			int x=n2;
			for(l=j;l>=j-n2+1;l--)
			{
				sx=sx+a[i][l]-a[i-x][l-x];
				x--;
			}
			if(sx<smin)
				smin=sx;
		}
	printf("%d\n",s-smin);
}

int main()
{
	read();
	work();
	return 0;
}