#include<stdio.h>
int n,k,a[5000010],dq[5000010],st=1,dr;
long long sum;
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]);
	for(i=1;i<=n;i++)
	{
        while(st<=dr && a[i]<=a[dq[dr]]) dr--;
        dq[++dr]=i;
		if(dq[st]==i-k) st++;
		if(i>=k) sum+=a[dq[st]];
	}
	printf("%lld\n",sum);
	return 0;
}