#include <fstream>
#include <cstdio>
#define VAL 1005
#define INF 0x3f3f3f3f

using namespace std;

int N, K, i, j;
int sum, v[VAL][VAL];
int col[VAL][VAL], mn;
int lin[VAL][VAL];
int diag[VAL][VAL];
int dp[VAL][VAL], l, c;

int main()
{
    freopen("ferma2.in", "r", stdin);
    freopen("ferma2.out", "w", stdout);
    scanf("%d %d", &N, &K);
    l=c=N-K;
    K=l;
    mn=INF;
    for (i=1; i<=N; i++)
    {
        for (j=1; j<=i; j++)
        {
            scanf("%d", &v[i][j]);
            col[i][j]=col[i-1][j]+v[i][j];
            lin[i][j]=lin[i][j-1]+v[i][j];
            diag[i][j]=diag[i-1][j-1]+v[i][j];
            sum+=v[i][j];
            if (i==l && j==c)
            {
                dp[i][j]=sum;
                mn=dp[i][j];
            }
        }
    }
    for (i=l+1; i<=N; i++)
    {
        for (j=c; j<=i; j++)
        {
            if (j!=i)
              dp[i][j]=dp[i-1][j]+(lin[i][j]-lin[i][j-K])-(diag[i-1][j]-diag[i-1-K][j-K]);
            else
              dp[i][j]=dp[i][j-1]-(col[i][j-K]-col[i-K][j-K])+(diag[i][j]-diag[i-K][j-K]);
            mn=min(mn, dp[i][j]);
        }
    }
    if (mn==INF)
      mn=sum;
    printf("%d\n", sum-mn);
    return 0;
}