# include <cstdio>
# include <deque>
using namespace std;
int i,j,n,k;
long long VV;
int v[5000005];
deque <int> d;
int main ()
{
    freopen ("deque.in", "r", stdin);
    freopen ("deque.out", "w", stdout);
    scanf ("%d%d", &n, &k);
    for (i=1; i<=n; ++i)
    {
        scanf ("%d", &v[i]);
        while (!d.empty () && v[i]<v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (d.front()==i-k) d.pop_front ();
        if (i>=k) VV+=v[d.front()];
    }
    printf ("%lld\n", VV);

    return 0;
}