#include <cstdio>
#include <algorithm>
#define INF 2000000000
#define Nmax 1005

using namespace std;

int a[Nmax][Nmax],dg[Nmax][Nmax],l[Nmax][Nmax],c[Nmax][Nmax],dp[Nmax][Nmax];

int main()
{
    int i,j,s=0,N,K,sol=INF;
    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]);
            s+=a[i][j];
        }
    K=N-K;
    for(i=1;i<=N;++i)
        for(j=1;j<=N;++j)
        {
            l[i][j]=l[i][j-1]+a[i][j];
            c[i][j]=c[i-1][j]+a[i][j];
            dg[i][j]=dg[i-1][j-1]+a[i][j];
        }
    for(i=1;i<=K;++i)
        for(j=1;j<=i;++j)
            dp[K][K]+=a[i][j];
    for(j=K+1;j<=N;++j)
        dp[K][j]=dp[K][j-1]+dg[K][j]-c[K][j-K];
    for(i=K+1;i<=N;++i)
        for(j=K;j<=N;++j)
            dp[i][j]=dp[i-1][j]-(dg[i-1][j]-dg[i-K-1][j-K])+(l[i][j]-l[i][j-K]);

    for(i=K;i<=N;++i)
        for(j=K;j<=i;++j)
            sol=min(sol,dp[i][j]);
    printf("%d\n", s-sol);
    return 0;
}