//#define WYTE 133
#include<bits/stdc++.h>
#define X first
#define Y second
#define mp(x,y) make_pair((x),(y))
#define pb(x) push_back(x)
#define eb emplace_back
#define ALL(x) (x).begin(),(x).end()
#define INIT(x,y) memset((x),(y),sizeof(x))
#define arrayin(a,n) for(int i=0;i<n;i++){cin>>a[i];}
#define arrayin1(a,n) for(int i=1;i<=n;i++){cin>>a[i];}
#define PQ priority_queue
#define IT iterator
#define INF 1e9
#define LLNF 1e18
#define EPS 1e-9
#define MOD 1000000007
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vii;

int n,k,c[10005];
ll memo[10005];
ll dp(int idx)
{
    if(idx>n)return 0;
    if(memo[idx]==-1)
    {
        memo[idx]=LLNF;
        for(int i=idx;i<=idx+k&&i<=n;i++)
        {
            memo[idx]=min(memo[idx],c[i]+dp(i+k+1));
        }
    }
    return memo[idx];
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>n>>k;
    arrayin1(c,n);
    INIT(memo,-1);
    cout<<dp(1)<<'\n';
}