#include <stdio.h>
#define dim 1000

int a[dim][dim],n,k;

int smin()
{
    int l,c,i,j,sum,min=0;
    for(l=0;l<=n-k+1;l++)
    {
        for (c=0;c<=l;c++)
        {
            sum=0;
            for(i=0;i<k-1;i++)
                for(j=0;j<=i;j++)
                    sum+=a[l+i][c+j];
            //printf("%d ",sum);
            if((sum<min)||(min==0))
                min = sum;
        }
        //printf("\n");
    }
    return min;
}

int main()
{
    int i,j,total=0;
    freopen("ferma2.in","r",stdin);
    freopen("ferma2.out","w",stdout);
    scanf("%d %d",&n,&k);
    for (i=0;i<n;i++)
        for (j=0;j<=i;j++)
        {
            scanf("%d",&a[i][j]);
            total+=a[i][j];
        }
    printf("%d\n",total-smin());
    return 0;
}