#include <deque>
#include <fstream>
using namespace std;
deque <int> dq,pos;
int main ()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n,k;
    fin>>n>>k;
    int nr;
    for (int i=1;i<=k;++i)
    {
        fin>>nr;
        while (!dq.empty() && dq.back()>=nr)
        {
            dq.pop_back();
            pos.pop_back();
        }
        dq.push_back(nr);
        pos.push_back(i);
    }
    long long int s=dq.front();
    for (int i=k+1;i<=n;++i)
    {
        fin>>nr;
        if (pos.front()==i-k)
        {
            pos.pop_front();
            dq.pop_front();
        }
        while (!dq.empty() && dq.back()>nr)
        {
            pos.pop_front();
            dq.pop_front();
        }
        dq.push_back(nr);
        pos.push_back(i);
        s+=dq.front();
    }
    fout<<s;
}