#include <fstream>
#include <deque>

using namespace std;

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

deque<int> q;

int n,k,u,p,v[5000005],i;

//deq[5000005]

long long s;

int main()
{
    fin >> n >> k ;

    for (i=1;i<=n;i++) fin >> v[i];



    for (i=1;i<=n;i++)
    {
        while (!q.empty() && v[i] <= v[ q.back() ] )
        {
            //--u;
            q.pop_back();
        }

        //deq[++u]=i;

        q.push_back(i);

        if (q.front()==i-k)
        {
            //p++;
            q.pop_front();
        }

        if (i>=k)
        {
            s=s+v[q.front()];
        }
    }
    fout << s <<endl;

    return 0;
}