#include<bits/stdc++.h>
using namespace std;
 
#define sd(mark) scanf("%d",&mark)
#define ss(mark) scanf("%s",&mark)
#define sl(mark) scanf("%lld",&mark)
#define debug(mark) printf("check%d\n",mark)
#define clr(mark) memset(mark,0,sizeof(mark))
#define F first
#define S second
#define MP make_pair
#define PB push_back
#define ll long long
#define INF 1e16
#define N 10010
#define K 1010

ll dp[N],c[N];
ll minn[N],postmin[N];
int n;
void updatepost()
{
	postmin[n] = minn[n];
	for(int i=n-1;i>=0;--i)
		postmin[i] = min(postmin[i+1],minn[i]);
}

int main()
{
	int k,i,j;
	sd(n);sd(k);
	for(i=1;i<=n;++i)
		sl(c[i]);
	for(i=0;i<=n;++i)
		minn[i]=INF;
	minn[0]=0;
	updatepost();
	for(i=1;i<=n;++i)
	{
		for(j=0;j<=n;++j)
			dp[j] = minn[j];

		int hi = min(n,i+k);
		int lo = max(1,i-k);

		dp[hi] = min(dp[hi],postmin[lo-1]+c[i]);
		minn[hi] = min(minn[hi],dp[hi]);
		updatepost();
	}
	printf("%lld\n",minn[n]);
}