#include<fstream>
#include<algorithm>

using namespace std;

#define val first
#define poz second

ifstream f("deque.in");
ofstream g("deque.out");

const int Nmax = 5000001;

int N, K, M, nr;
pair<int, int> Heap[Nmax];
long long rez;

void Heap_Up(int k) {
    while(k>1 && Heap[k/2].val > Heap[k].val) {
        swap(Heap[k], Heap[k/2]);
        k/=2;
    }
}

void insert(pair<int, int> elem) {
    Heap[++M] = elem;
    Heap_Up(M);
}

void Heap_Down(int k) {
    int son = k;
    if(2*k <= M && Heap[2*k].val < Heap[son].val)
        son = 2*k;
    if(2*k+1 <= M && Heap[2*k+1].val < Heap[son].val)
        son = 2*k+1;
    if(son!=k) {
        swap(Heap[k], Heap[son]);
        Heap_Down(son);
    }
}

void erase(int k) {
    Heap[k] = Heap[M];
    --M;
    Heap_Down(k);
}

int main() {

    int i;
    pair<int, int> elem;

    f>>N>>K;

    for(i=1; i<=N; ++i) {
        f>>nr;
        elem.val = nr;
        elem.poz = i;
        insert(elem);
        while(M && Heap[1].poz <= i-K)
            erase(1);
        if(i>=K)
            rez+=Heap[1].val;
    }

    g<<rez<<"\n";

    f.close(); g.close();

    return 0;
}