#include<bits/stdc++.h>
using namespace std;
#define fs first
#define sc second
#define MAX 100000
#define pb push_back
#define mp make_pair
#define INF (1LL<<62)
#define MOD 1000000007
typedef long long Int;
typedef pair<Int,Int> pii;
typedef vector<Int> vi;
typedef vector<pii> vii;
Int c[10004],n,k;
int main()
{
    Int ans=INF;
    cin>>n>>k;
    k++;
    for (Int i=0;i<n;++i)
        cin>>c[i];
    for (Int i=n-1;i>=n-k-1;--i)
    {
        Int curr=0;
        for (Int j=i;j>=0;j-=2*k-1)
            curr+=c[j];
        ans=min(ans,curr);
    }
    cout<<ans;
    return 0;
}