#include <iostream>
#include <algorithm>
#include <map>
#include <vector>
#include <set>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
#define Boost ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define pb push_back
#define mp make_pair

const int inf = 2147483647;
const int MOD = 1e9+7;
const int MAXN = 1e5+9;

ll a[MAXN];

ll solve(ll n,ll k){
    if(n<0)
        return 0;
    if(n==0)
        return a[n];
    return min(solve(n-k-1,k) + a[n],solve(n-1,k));
}

int main() {
//    Boost;
    ll n,k;
    cin>>n>>k;
    for (int i = 0; i < n; ++i) {
        cin>>a[i];
    }
    cout<<solve(n-1,k);
    return 0;
}