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