#include<stdio.h>
#define max 5000010
int n,k;
int A[max],Coada[max];
int cap,spate;
long long suma;
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]);
	cap=1;spate=0;
	for(i=1;i<=n;i++)
	{
		while(cap<=spate&&A[i]<=A[Coada[spate]])
			spate--;
		Coada[++spate]=i;
		if(Coada[cap]==i-k)
			cap++;
		if(i>=k)
			suma+=A[Coada[cap]];
	}
	printf("%lld",suma);
	return 0;
}