#include <cstdio>
#include <deque>

#define pb push_back
#define f front
#define pf pop_front
#define pbb pop_back

using namespace std;

typedef struct
{
    int a, b;
} nod;

deque <nod> d;

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

    int n, k;
    scanf ("%d %d", &n, &k);

    int x;
    scanf ("%d", &x);

    nod xx;
    xx.a = x;
    xx.b = 1;

    d.pb (xx);

    long long s = 0;

    for (int i = 2; i <= k; i++)
    {
        scanf ("%d", &x);
        while (d.size () && x < d[d.size() - 1].a)
            d.pbb ();

        xx.a = x;
        xx.b = i;

        d.pb (xx);
    }

    s += d[0].a;

    for (int i = k + 1; i <= n; i++)
    {
        while (d[0].b <= i - k && d.size ())
            d.pf ();

        scanf ("%d", &x);

        while (d.size () && x < d[d.size() - 1].a)
            d.pbb ();

        xx.a = x;
        xx.b = i;

        d.pb (xx);

        s += d[0].a;
    }

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

    return 0;
}