#include <iostream>
#include <cstdio>
#define MAXN 5000050

using namespace std;

int n, k, a[MAXN], rez;
int deck[MAXN], st=1, dr;
long long sum;

void add(int nr)
{
    while (dr && a[nr] < a[deck[dr]]) dr--;
    deck[++dr] = nr;
}

int get(int nr)
{
    while (deck[st] <= nr-k)
		st++;
    return deck[st];
}

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", &a[i]);
    for (int i = 1; i <= k-1; i++)
		add(i);
    for (int i = k; i <= n; i++) {
		add(i);
		int rez = a[get(i)];
		sum += rez;
    }
    printf("%lld", sum);

    return 0;
}