#include<cstdio>
int a[1001][1001],i,j,sum,n,m,k,b[1001][1001];
int main ()
{
freopen("ferma2.in","r",stdin);
freopen("ferma2.out","w",stdout);
scanf("%d%d",&n,&k);
for(i=1;i<=n;i++)
    for(j=1;j<=i;j++)
        {
        scanf("%d",&a[i][j]);
        b[i][j]=a[i][j]+b[i-1][j-1];
        sum+=a[i][j];
        }
int s=n-k,smin=1000000000;
for(i=s;i<=n;i++)
    for(j=s;j<=i;j++)
        {
        int ss=0;
        for(int q=j;q>=j-s+1;q--)
            ss+=b[i][q]-b[i-s+j-q][q-s+j-q];
        if(ss<smin)
            smin=ss;
        }
printf("%d",sum-smin);
return 0;
}