#include<iostream>
#include<atcoder/segtree>
using namespace std;
long op(long a,long b){return max(a,b);}
long e(){return -1e18;}
int N,K,A[2<<17];
long S[2<<17];
main()
{
	cin>>N>>K;
	K--;
	for(int i=0;i<N;i++)
	{
		cin>>A[i];
		S[i+1]=S[i]+A[i];
	}
	atcoder::segtree<long,op,e>seg(N+2);
	seg.set(0,0L);
	long ans=0;
	for(int i=1;i<=N;i++)
	{
		long now=seg.prod(max(i-K,0),i)+S[i];
		ans=max(ans,now);
		seg.set(i,op(seg.get(i),seg.get(i-1)+S[i-1]-S[i]));
		seg.set(i+1,now-S[i+1]);
	}
	cout<<ans<<endl;
}