#include <cstdio>

using namespace std;

typedef struct
{
    int a, b;
} nod;

nod d[5000010];

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

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

    int x, p = 0, pp = 1;
    scanf ("%d", &x);

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

    d[++p] = xx;

    long long s = 0;

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

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

        d[++p] = xx;
    }

    s += d[pp].a;

    for (int i = k + 1; i <= n; i++)
    {
        while (d[pp].b <= i - k && p >= pp)
            pp++;

        scanf ("%d", &x);

        while (x < d[p].a && p >= pp)
            p--;

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

        d[++p] = xx;

        s += d[pp].a;
    }

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

    return 0;
}