#include <fstream>
#include <deque>
using namespace std;
deque <pair<int,int> >a;
pair<int,int>x,y;
long long v,i,j,m,n,k;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    f>>n>>k;
    for (i=1; i<=n; i++)
    {
        f>>v;
        while (a.size() && v<a.back().first) a.pop_back();
        a.push_back(make_pair(v,i));
        if (i>=k) m+=a.front().first;
        if (i-a.front().second +1 >= k)
                       a.pop_front();
    }
    g<<m;
    f.close();
    g.close();
    return 0;
}