#include <fstream>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int i,n,q[5000001],v[5000001],nr,u,p,k;
long long s;
int main()
{
    f>>n>>k;

    for(i=1;i<=n;i++)
        f>>v[i];
    q[1]=1;
    u=p=1;
    for(i=2;i<=n;i++){
    while(v[i]<=v[q[u]]&&p<=u)
        u--;
        q[++u]=i;
   if(q[p]==i-k)
    p++;
    if(i>=k)
        s+=v[q[p]];
    }
    g<<s;

    return 0;
}