#include <fstream>

using namespace std;

ifstream fin("ferma2.in");
ofstream fout("ferma2.out");

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

int main()
{
	fin>>N>>K;
	for(int i = 1 , val;i <= N;++i) {
		for(int j = 1;j <= i;++j){
			fin>>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 = max(ans,totalSum - sum);
		}
	}
	fout<<ans;
	return 0;
}