#include <fstream>
#define nmax 5000004

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int Deque[nmax];
int V[nmax];
int L,S,N,K,sum;

int main()
{
    int i;
    in>>N>>K;
    S=1;
    for(i=1;i<=N;i++)
    {
        in>>V[i];
        //il plasez in deque
        while(L>=S&&V[Deque[L]]>V[i])L--;
        Deque[++L]=i;
        while(i-Deque[S]>=K)S++;
        if(i>=K)
            sum+=V[Deque[S]];
    }
    in.close();
    out<<sum<<'\n';
    out.close();
    return 0;
}