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