#include <cstdio>

const int NMAX = 1002;
int N , K , s[NMAX][NMAX] , ans , totalSum;

int main()
{
	freopen("ferma2.in","r",stdin);
	freopen("ferma2.out","w",stdout);
	scanf("%d %d",&N,&K);
	for(int i = 1 , val;i <= N;++i) {
		for(int j = 1;j <= i;++j){
			scanf("%d",&val);
			totalSum+=val;
			s[i][j] = s[i - 1][j - 1] + val;
		}
	}

	K = N - K;
	for(int i = 1;i <= N;++i) {
		for(int j = 1;j + K - 1 <= i;++j) {
			int sum = 0;
			for(int k = 0;k < K;++k) {
				sum+=s[i][j + k] - s[i - k - 1][j - 1];
			}
			ans = ans > totalSum - sum ? ans : totalSum - sum;
		}
	}
	printf("%d\n",ans);
	return 0;
}