#include<stdio.h>
const int N=5000001;
int i,n,k,start,end,v[N],deque[N];
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",&v[i]);
	start=1;
	end=0;
	for(i=1;i<=n;++i)
	{
		while(start<=end&&v[deque[end]]>=v[i]) --end;
		deque[++end]=i;
		if(deque[start]==i-k) ++start;
		if(i>=k) s+=v[deque[start]];
	}
	printf("%lld\n",s);
	return 0;
}