#include <fstream>
#include <deque>

using namespace std;

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

deque <int> dq;

int n,k,a[500001];
long long s;

int main()
{
    f>>n>>k;
    for (int i=1;i<=n;i++)
        f>>a[i];
    for (int i=1;i<=n;i++)
    {
        if (!dq.empty() && dq.front()==i-k)
            dq.pop_front();
        while (!dq.empty() && a[dq.back()]>=a[i])
            dq.pop_back();
        dq.push_back(i);
        if (i>=k)
            s+=a[dq.front()];
    }
    g<<s;
}