#include<cstdio>
#define Nmax 1024
using namespace std;

char v[Nmax][Nmax];
unsigned int sc[Nmax][Nmax],N,K,L,F,m,S;

int main(){
	
	freopen("ferma2.in","r",stdin);
	freopen("ferma2.out","w",stdout);
	
	scanf("%d%d",&N,&K);
	
	for(unsigned int i=1;i<=N;++i)
		for(unsigned int j=1;j<=i;++j){
			scanf("%d",&m);
			v[i][j]=m;
			S+=v[i][j];
			sc[i][j]=sc[i-1][j]+v[i][j];
	}
		
	L=N-K;
	F=N-L+1;
	m=0x3f3f3f3f;
	
	for(unsigned int l=1;l<=F;++l)
		for(unsigned int j=1;j<=F&&j<=l;++j){
			
			unsigned int s=0;
			
			for(unsigned int p=j;p<j+L;++p)
				s+=sc[l+L-1][p]-sc[l+p-j-1][p];
			
			if(s<m)
				m=s;
			
		}
	printf("%d",S-m);
return 0;
}