#include <fstream>
#include <deque>

using namespace std;

deque <int> dublcoada;
deque <int> pminim;

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

int n,k,pdeadunat,nr,i;
long long suma;

int main()
{
    f>>n>>k;
    pdeadunat=k;
    for(i=1;i<=n;i++)
    {
        f>>nr;
        if(dublcoada.empty()!=0)
        {
            dublcoada.push_back(nr);
            pminim.push_back(i);
        }
        else
        {
            while(nr<=dublcoada.back())
            {
                dublcoada.pop_back();
                pminim.pop_back();
                if(dublcoada.empty()!=0)
                    break;
            }

            dublcoada.push_back(nr);
            pminim.push_back(i);
        }
        if(i>=k)
            suma+=dublcoada.front();
        if(pminim.front()==i+1-k)
        {
            dublcoada.pop_front();
            pminim.pop_front();
        }
    }

    g<<suma;

    return 0;
}