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

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

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

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

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

        d.push_back(i);

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

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