#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
int d[5000001],v[5000001],front,back,s,i,n,k;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    front=back=1;
    for(int i=1;i<=n;i++)
    {
        while(front<=back && v[i]<=v[d[back]])
            back--;
        d[++back]=i;
        if(i-k == d[front])
            front++;
        if(i>=k)
            s=s+v[d[front]];
    }
    g<<s;
    return 0;
}