#include<cstdio>
#include<deque>
using namespace std;
int n,k,i,x; long long s;
deque<pair<int,int> > q;
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",&x);
	    while(!q.empty() && x<q.back().first) q.pop_back();
	    q.push_back(make_pair(x,i));
	    if(q.front().second==i-k) q.pop_front();
	    if(i>=k) s+=q.front().first;
	}
	printf("%lld\n",s);
	return 0;
}