# include <fstream>
# include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> d;
int i,j,n,m,k;
int v[5000005];
long long S;
int main ()
{
    f>>n>>k;
    for (i=1; i<=n; ++i)
    {
        f>>v[i];
        while (! d.empty() && v[i]<=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (d.front()==i-k) d.pop_front();
        if (i>=k) S+=v[d.front()];
    }
    g<<S<<"\n";

    return 0;
}