#include <fstream>
#include <queue>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");

int n, i, a[5000001], k;
long long s;
deque<int>q;

int main ()
{
    f >> n >> k;

    for (int i=1; i<=n; i++)
        f >> a[i];

    for (int i=1; i<=n; i++)
    {
        while (!q.empty() && a[i]<=a[q.back()])
            q.pop_back();

        q.push_back(i);

        if (q.front()==i-k) q.pop_front();
        if (i>=k) s+=a[q.front()];
    }
    g << s;
    return 0;
}