#include <deque>
#include <fstream>

using namespace std;

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

deque<int>dq;
int n,k;
long long sum;

int main()
{
    in>>n>>k;
    int*v=new int[n];
    for(int i=0; i<n; i++)
    {
        in>>v[i];
    }
    in.close();
    for(int i=0; i<n; 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()];
        }
    }
    out<<sum;
    out.close();
    return 0;
}