#include <fstream>
#include <deque>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n, sum, k, a[5000010];
deque < int > C;

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

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

        C.push_back(i);

        if (C.front()==i-k) C.pop_front();
        if (i>=k) sum+=a[C.front()];
    }

    g<<sum<<'\n';
    return 0;
}