#include<stdio.h>
int q[5000001];
int x[5000001];
int main()
{
	freopen("d.in","r",stdin);
	freopen("d.out","w",stdout);
	int n,k,p,u,i,min=0;
	long long s=0;
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;i++)
		scanf("%d",&x[i]);
	p=1;
	u=0;
	for(i=1;i<=n;i++)
	{
		while(p<=u && x[i]<=x[q[u]])
			u--;
		q[++u]=i;
		if(i-q[p]==k)
			p++;
		if(i>=k)
			s=s+x[q[p]];
	}
	printf("%lld\n",s);
	return 0;
}