#include<fstream>
#define X 1<<10
using namespace std;
ifstream f("ferma2.in");
ofstream g("ferma2.out");
int n,k,i,j,x,sum,mini=1e9,L[X][X],R[X][X],T[X][X];
int main ()
{
    f>>n>>k;
    for(i=1;i<=n;++i)
        for(j=1;j<=i;++j)
    {
        f>>x;
        sum+=x;
        L[i][j]=L[i][j-1]+x;
        R[i][j]=R[i-1][j]+L[i][j];
        T[i][j]=T[i-1][j-1]+L[i][j];
    }
    k=n-k;
    for(i=k;i<=n;++i)
        for(j=k;j<=i;++j)
            mini=min(mini,T[i][j]-R[i][j-k]+R[i-k][j-k]-T[i-k][j-k]);
    g<<sum-mini;
    return 0;
}