//selling.cpp
#include<cstdio>
#include<climits>
#include<algorithm>
#include<deque>
#include<vector>
#include<utility>
using namespace std;

void sgt_init(vector<int> &sgt, vector<int> &no, int id, int l, int r)
{
	sgt[id] = INT_MIN;
	if(l == r)
	{
		no[l] = id;
		return;
	}
	int mid = (l + r) >> 1;
	sgt_init(sgt, no, id << 1, l, mid);
	sgt_init(sgt, no, id << 1 | 1, mid + 1, r);
	return;
}

void sgt_update(vector<int> &sgt, int id, int val)
{
	sgt[id] = val;
	id >>= 1;
	while(id)
	{
		sgt[id] = max(sgt[id << 1], sgt[id << 1 | 1]); 
		id >>= 1;
	}
	return;
}

int sgt_query(vector<int> &sgt, int id, int x, int y, int l, int r)
{
	if(x > r || y < l)
	{
		return INT_MIN;
	}
	if(x >= l && y <= r)
	{
		return sgt[id];
	}
	int mid = (x + y) >> 1;
	return max(sgt_query(sgt, id << 1, x, mid, l, r), sgt_query(sgt, id << 1 | 1, mid + 1, y, l, r));
}

int solve(int n, int d, vector<int> &p)
{
	vector<int> sgt(n * 5);
	vector<int> no(n);
	
	sgt_init(sgt, no, 1, 0, n - 1);
	sgt_update(sgt, no[0], 0);
	
	for(int i = 1; i < n; ++i)
	{
		sgt_update(sgt, no[i], sgt_query(sgt, 1, 0, n - 1, max(i - d, 0), i - 1) + p[i]);
	}
	return sgt[no[n - 1]];
}

int main()
{
	int n, d;
	vector<int> p;
	scanf("%d%d", &n, &d);
	p.resize(n, 0);
	for(int i = 1; i < n - 1; ++i)
	{
		scanf("%d", &p[i]);
	}
	printf("%d\n", solve(n, d, p));
	return 0;
}