/*
        SUPTO
        UNIVERSITY OF DHAKA
*/
#include <bits/stdc++.h>
using namespace std;
#define D(x) cerr<<#x " = "<<(x)<<endl
#define pb push_back
#define ff first
#define ss second
#define mem(a) memset(a,0,sizeof(a))
#define _set(a) memset(a,-1,sizeof(a))
typedef long long int ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define eps 1e-9
#define MAX 100005
#define MAXL 20
#define MAXE 100000
//const int mod = 100000007;
//int dx[] = {0,0,1,-1};
//int dy[] = {1,-1,0,0};
//int dx[] = {-1,-1,-1,0,0,1,1,1};
//int dy[] = {-1,0,1,-1,1,-1,0,1};
const ll inf = 1LL<<60;
ll c[1005], lft[1005], rgt[1005], mx[1005];
int main()
{
    int n , k, i, j;
    scanf("%d %d", &n, &k);
    for(i = 1; i <= n; i++) scanf("%lld", &c[i]);
    lft[0] = 0;
    for(i = 1; i <= n; i++)
    {
        lft[i] = inf;
        for(j = i; j > 0 && i-j <= k; j--)
        {
            lft[i] = min(lft[i], c[j]+lft[max(0, j-k-1)]);
        }
    }
    rgt[n+1] = 0;
    for(i = n; i > 0; i--)
    {
        rgt[i] = inf;
        for(j = i; j <= n && j-i <= k; j++)
        {
            rgt[i] = min(rgt[i], c[j]+rgt[min(n+1, j+k+1)]);
        }
    }
    ll ans = inf;
    for(i = 1; i <= n; i++)
    {
        ans = min(ans, c[i]+lft[max(0, i-k-1)]+rgt[min(n+1, i+k+1)]);
        for(j = i; j > 0 && i-j <= k; j--)
        {
            ans = min(ans, c[j]+lft[max(0, j-k-1)]+rgt[min(n+1, j+k+1)]);
        }
        for(j = i; j <= n && j-i <= k; j++)
        {
            ans = min(ans, c[j]+rgt[min(n+1, j+k+1)]+lft[max(0, j-k-1)]);
        }
    }
    printf("%lld\n", ans);
    return 0;
}