#include <fstream>
#include <deque>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

deque <int> c;
int v[5000010],n,k,i;
long long s;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
    }
    s=0;
    c.push_front(1);
    for(i=2;i<=n;i++)
    {
        while(v[i]<v[c.back()] && c.empty()==0)
        {
            c.pop_back();
        }
        c.push_back(i);
        if(i-k>=c.front())
        {
            c.pop_front();
        }
        if(i>=k)
            s+=v[c.front()];
    }
    g<<s;
    return 0;
}