#include <cstdio>
#define NMax 1000
#define INF 1<<30

int prc[NMax+1][NMax+1];
int col[NMax+1][NMax+1];
int lin[NMax+1][NMax+1];
int a[NMax+1][NMax+1];
int N,K,ans,minim=INF;

void Precalc()
{
    int i,j;

    for(i = 1; i <= N; ++i)
        for(j = 1; j <= i; ++j)
        {
            prc[i-j][j] = prc[i-j][j-1] + a[i][j];
            col[j][i] = col[j][i-1] + a[i][j];
            lin[i][j] = lin[i][j-1] + a[i][j];
            ans += a[i][j];
        }
}

int main(){
    freopen("ferma2.in","r",stdin);
    freopen("ferma2.out","w",stdout);

    int i,j,L,first,temp;

    scanf("%d %d",&N,&K);
    for(i = 1; i <= N; ++i)
        for(j = 1; j <= i; ++j) scanf("%d",&a[i][j]);

    Precalc();

    L = N-K; first = 0;
    for(i = 1; i <= L; ++i) first += prc[i-1][L-i+1];
    minim = first;

    for(i = 2; i <= N-L+1; ++i)
    {
        first = first - prc[i-2][L] + lin[i+L-1][L];

        temp = first;
        if( temp < minim ) minim = temp;

        for(j = 2; j <= i; ++j)
        {
            temp = temp - ( col[j-1][i+L-1] - col[j-1][i-1] ) + ( prc[i-j][j+L-1] - prc[i-j][j-1] );
            if( temp < minim ) minim = temp;
        }
    }

    printf("%d\n", ans-minim );



return 0;
}