#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;

int main() {
	int n;
	int k;
	long long result=0;
	cin >> n >> k;	
	vector<int> data(n);
	vector< pair<int,int> >	mincost(n);
	for (int i=0;i<n;i++)
		cin >> data[i];
	for (int i=0;i<n;i++)
	{
		int l=max(i-k,0);
		int r=min(i+k+1,n);
		int min_c=1000000000;
		int min_i=i;
		for (int j=l;j<r;j++)
		{
			if (data[j] < min_c)
			{
				min_c=data[j];
				min_i=j;
			}
			mincost[i]=make_pair(min_i,i);
		}
	}
	sort(mincost.begin(),mincost.end());
	for (int i=n-1; i>=0;i--)
	{
		int idx=mincost[i].second;
		if (data[idx] != 0)
		{
			result+=mincost[i].first;
			int l=max(idx-k,0);
			int r=min(idx+k+1,n);
			for (int j=l;j<r;j++)
			{
				data[j]=0;
			}
		}
	}
	
		
	cout << result << endl;
	return 0;
}