#include<stdio.h>
int A[5000001], i, head, tail, k, n, a,deque[5000001];
long long s;
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]);
	head=1 ; tail=0;
	for(i=1;i<=n;i++){
		while(head<=tail && A[i]<=A[deque[tail]])
			tail--;
	deque[++tail ]=i;
	if (deque[head]==i-k)head++;
	if (i>=k) s+=A[deque[head]];
	}
	printf ("%lld\n",s);
	return 0;
	
}