#include <cstdio>
#include <cstdlib>

using namespace std;

struct deq_el
{
    int poz, val;
    deq_el *next, *prev;
};

struct deq
{
    deq_el *cap, *coada;
};

bool isempty(deq d)
{
    return d.cap == 0;
}

void insert_front(deq &d, int val, int poz)
{
    if(d.cap == 0)
    {
        d.cap = (deq_el*) malloc(sizeof(deq_el));

        d.cap->prev = d.cap->next = 0;
        d.cap->val = val;
        d.cap->poz = poz;

        return;
    }
    deq_el * cr = (deq_el*) malloc(sizeof(deq_el));

    cr->prev = 0;
    cr->next = d.cap;

    cr->val = val;
    cr->poz = poz;

    d.cap->prev = cr;
    d.cap = cr;
}

void insert_back(deq &d, int val, int poz)
{
    if (!d.cap)
    {
        insert_front(d, val, poz);
        return;
    }

    deq_el * cr = (deq_el*) malloc(sizeof(deq_el));
    cr->next = 0;

    cr->val = val;
    cr->poz = poz;

    if(d.coada)
    {
        d.coada->next = cr;
        cr->prev = d.coada;
        d.coada = cr;
    }
    else
    {
        d.coada = cr;
        cr->prev = d.cap;
        d.cap->next = cr;
    }

}


void delete_front(deq &d)
{
    if(!d.cap)
        return;
    if (d.cap->next)
    {
        deq_el *cr = d.cap;

        d.cap = d.cap->next;
        d.cap->prev = 0;
        free(cr);
        if(d.cap == d.coada)
        {
            d.coada = 0;
            d.cap->next = d.cap->prev = 0;
        }
        return;
    }

    free(d.cap);
    d.cap = 0;
}


void delete_back(deq &d)
{
    if (!d.coada)
    {
        delete_front(d);
        return;
    }

    if (d.coada->prev == d.cap)
    {
        d.cap->next = 0;
        free(d.coada);
        d.coada = 0;
        return;
    }
    deq_el *cr;
    cr = d.coada;
    d.coada = d.coada->prev;
    d.coada->next = 0;
    free(cr);
}


void clean_deq(deq &d, int min_poz)
{
    while(!isempty(d) && d.cap->poz < min_poz)
        delete_front(d);
}

void insert_deq(deq &d, int val, int poz)
{
    while(!isempty(d) && d.coada && val <= d.coada->val)
        delete_back(d);
    if (d.cap && val <= d.cap->val)
        delete_front(d);
    insert_back(d, val, poz);
}

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    int n, m, i, x, s = 0;
    scanf("%d%d", &n, &m);

    deq d;
    d.cap = d.coada = 0;

    for(i=1; i<m; ++i)
    {
        scanf("%d", &x);
        insert_deq(d, x, i);
    }
    for(i=m; i<=n; ++i)
    {
        scanf("%d", &x);
        clean_deq(d, i-m+1);
        insert_deq(d, x, i);

        s += d.cap->val;
    }

    printf("%d\n", s);

    fclose(stdin);
    fclose(stdout);
    return 0;
}