#include<stdio.h>
int deque[5000010],cnt[5000010];
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	int i,n,u,nr,k,a,p;
	long long s;
	s=0;
	scanf("%d%d",&n,&k);
	p=1; u=0; nr=0;
	for(i=1;i<=n;i++)
		{
			scanf("%d",&a);
			while(p<=u && a<=deque[u])
				u--;
			
			deque[++u]=a;
			cnt[u]=i;
			if(cnt[u]-cnt[p]==k)
				p++;
			if(i>=k) 
				s+=deque[p];
    	}
	printf("%lld",s);
	return 0;
}