//longlong5a6
#include <bits/stdc++.h>
#define pii pair<int,int>
#define F first
#define S second
#define bit(i, x)((x >> i) & 1)
#define sobit(i)  __builtin_popcount((int)(i))
#define pb push_back
#define all(x) x.begin(),x.end()
#define vi vector<int>
#define For(i,x,n) for(int (i)=(int)(x);(i)<=(int)(n);(i)++)
#define round(m,n) setprecision((int)m) << fixed << double(n)
#define down "\n"
#define TASK "hexangle"
#define maxn 3001

using namespace std;
int a[maxn][maxn];
int m;

void work(int k)
{
    if(k == 1)
    {
        return;
    }
    int sub;
    if(k == 2)
    {
        sub = 1;
    }
    else sub = ceil(1.0*k/1.5);
    work(sub);
    For(i, 1, m-k+1)
    {
        For(j, 1, i)
        {
            int lim = i - sub + k;
            a[i][j] = max(a[i][j], max(a[lim][j], a[lim][j-sub+k]));
        }
    }

}

int main()
{
    ios_base::sync_with_stdio(0);
        cin.tie();
        cout.tie();
    if (fopen("in.txt","r"))
        {
            freopen("in.txt","r",stdin);

        }
    if (fopen(TASK".INP","r"))
            {
                freopen(TASK".INP","r",stdin);
                freopen(TASK".OUT","w",stdout);
            }
    int k;
    cin>>m>>k;
    For(i,1,m)
    {
        For(j,1,i) cin>>a[i][j];
    }
    work(k);
    long long res=0;
    For(i,1,m-k+1)
    {
        For(j,0,i) res+=a[i][j];
    }
    cout<<res;
}