/* 
Dequeue.
*/

#include <iostream>
#include <stdio.h>

#define MAXN	5000000

int n, k;
int a[MAXN], dequeue[MAXN];
int front, back;
long long suma_minime;

void calculeaza_suma () {
	front = 1;
	back = 0;
	
	for (int i = 1; i <= n; i++) {
		while (front <= back && a[i] <= a[dequeue[back]])
			back--;
		back++;
		dequeue[back] = i;
		if (dequeue[front] == i - k) 
			front++;
		if (i >= k)
			suma_minime += a[dequeue[front]];
	}
}

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

	int i;
	scanf("%d %d", &n, &k);
	for (i = 1; i <= n; i++)
		scanf("%d", &a[i]);

	calculeaza_suma();

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

	return 0;
}