#include <fstream>
#include <deque>
#define mp make_pair
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int, int> >dq;
int n,k,v;
long long suma;
int main()
{
    f>>n>>k;
    for (int i = 1; i <= k; i++)
    {
        f>>v;
        pair<int, int>x = mp(v, i);
        while (!dq.empty() && dq.back().first > v )
        {
            dq.pop_back();
        }
        dq.push_back(x);

    }
    suma+=dq.front().first;
    for (int i = k + 1; i <= n; i++)
    {
        f>>v;
        while (dq.front().second <= i - k)
        {
            dq.pop_front();
        }
        pair<int, int>x = mp(v, i);
        while (!dq.empty() && dq.back().first > v)
        {
            dq.pop_back();
        }
        dq.push_back(x);
        suma+=dq.front().first;
    }
    g<<suma;
    return 0;
}