#include <stdio.h>

int a[5000000], deque[5000000];
int front, back,i,n,k;
long long suma;

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",&a[i]);
	suma=0;
	front=1; back=0;
	for (i=1; i<k; i++){
		for (; front<=back && a[i]<=a[deque[back]]; back--);
		back++;
		deque[back]=i;
		if (deque[front]+k==i)
			front++;
	}
	for (i=k; i<=n; i++){
		for (; front<=back && a[i]<=a[deque[back]]; back--);
		back++;
		deque[back]=i;
		if (deque[front]+k == i)
			front++;
		suma+=a[deque[front]];
	}
	printf("%lld\n",suma);
	fclose(stdin); fclose(stdout);
	return 0;
}