#include <bits/stdc++.h>
using namespace std;

#define FOR(i,l,r) for(int i = (l);i < (r);i++)
#define ALL(x) (x).begin(),(x).end()
template<typename T> void chmax(T& a,const T& b){if(a < b) a = b;}
template<typename T> void chmin(T& a,const T& b){if(b < a) a = b;}
typedef long long ll;

int N,K;
ll dp [10001];
const ll INF = 1e17;

int main()
{
	scanf("%d%d",&N,&K);
	vector<ll> C(N);
	FOR(i,0,N){
		scanf("%lld",&C [i]);
	}

	fill(dp,dp + N + 1,INF);
	dp [0] = 0;
	FOR(i,0,N){
		for(int j = max(0,i - K);j <= min(N - 1,i + K);j++){
			chmin(dp [min(j + K + 1,N)],dp [i] + C [j]);
		}
	}

	printf("%lld\n",dp [N]);

	return 0;
}