#include<stdio.h>

#define MaxN 2100

int N,K,T,SUM,MIN = 238923232,A[MaxN][MaxN],B[MaxN][MaxN],oriz[MaxN][MaxN],diag[MaxN][MaxN];

void citire(void)
{
	FILE *f = fopen("ferma2.in","r");
	
	fscanf(f,"%d %d",&N,&K);
	for(int i=1;i<=N;i++)
		for(int j=1;j<=i;j++)
		{
			fscanf(f,"%d ",&A[i][j]);
			SUM += A[i][j];
		}
	
	fclose(f);
}

void Bb(void)
{
	T = N-K;
	for(int i=N;i;i--)
		for(int j=1;j<=i;j++)
		{
			oriz[i][j] = A[i][j] + oriz[i][j-1];
			diag[i][j] = A[i][j] + diag[i+1][j+1];
			B[i][j] = B[i+1][j] - (oriz[i+T][j+T-1] - oriz[i+T][j-1]) + (diag[i][j]-diag[i+T][j+T]);
		}
}

int Min(void)
{
	for(int i=1;i<=N-T+1;i++)
		for(int j=1;j<=i;j++)
			if(MIN > B[i][j])
				MIN = B[i][j];
}

int main()
{
	FILE *g = fopen("ferma2.out","w");
	
	citire();
	Bb();
	Min();
	fprintf(g,"%d ",SUM-MIN);
	
	fclose(g);
	return 0;
}