#include <iostream>
#include <deque>

#define NMax 5000005

using namespace std;

int N, K, X[NMax];
deque <int> Deque;
long long S;

int main()
{
    freopen ("deque.in", "r", stdin);
    freopen ("deque.out", "w", stdout);
    scanf ("%d %d", &N, &K);
    for (int i=1; i<=N; ++i)
    {
        scanf ("%d", &X[i]);
        while (!Deque.empty () and X[Deque.back ()]>=X[i])
        {
            Deque.pop_back ();
        }
        Deque.push_back (i);
        if (Deque.front ()<=i-K)
        {
            Deque.pop_front ();
        }
        if (i>=K)
        {
            S+=X[Deque.front ()];
        }
    }
    printf ("%lld\n", S);
    return 0;
}