#include <fstream>
#include <deque>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n,k;
long long v[5000005];
deque<int>q;
long long suma;
void citire()
{
    int i;
    long long x;

    fin>>n>>k;

    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
}

void rezolvare()
{
    int i;
    deque<int>::iterator it;
    for(i=1;i<k;i++)
    {
        q.push_back(i);
    }
    for(i=k;i<=n;i++)
    {
        it=q.end()-1;
        while(q.size() && v[i]<=v[q.back()])
        {
            q.pop_back();
            it--;
        }
        q.push_back(i);
        if(i-k==q.front())
            q.pop_front();
        suma+=v[q.front()];


    }
    fout<<suma;

}

int main()
{

    citire();
    rezolvare();
    return 0;
}