#include<fstream>
#define N 5000005
using namespace std;

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

int n,k,deq[N],pozitii[N],st,dr,inc;
long long raspuns=0;
int main()
{

    fin>>n>>k;
    fin>>deq[dr++];
    for(int i=1; i<k; i++)
    {
        int element;
        fin>>element;
        while(st<dr&&element<deq[dr-1])
            dr--;
        deq[dr]=element;
        pozitii[dr++]=i;
    }
    raspuns+=deq[st];
    inc++;
    if(pozitii[st]<inc)
        st++;
    for(int i=k; i<n; i++)
    {
        int element;
        fin>>element;
        while(st<dr&&element<deq[dr-1])
            dr--;
        deq[dr]=element;
        pozitii[dr++]=i;
        raspuns+=deq[st];
        inc++;
        if(pozitii[st]<inc)
            st++;
    }
    fout<<raspuns;
    return 0;
}