#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> qe;
int v[5000001],i,n,k;
long long s;
int main()
{
    fin >>n>>k;
    for (i=1;i<=n;i++)
    {
        fin >>v[i];
    }
    for (i=1;i<=n;i++)
    {
        while (!qe.empty()&&v[i]<=v[qe.back()])
        {
            qe.pop_back();
        }
        qe.push_back(i);
        if (qe.front()==i-k) {qe.pop_front();}
        if (i>=k) {s=s+v[qe.front()];}
    }
    fout <<s;
    return 0;
}