#include <fstream>
#include <stack>
using namespace std;
deque<int> dq;
ifstream in ("deque.in");
ofstream out ("deque.out");
int n,v[10000001],k;
long long sum;
int main()
{
    in>>n>>k;
    for (int i=0; i<n; i++)
    {
        in>>v[i];
        if (!dq.empty() && dq.front()==i-k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && v[i]<=v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (i>=k-1)
        {
            sum+=v[dq.front()];
        }
    }
    in.close();
    out<<sum;
    out.close();
    return 0;
}