#include<bits/stdc++.h>
using namespace std;
deque<pair<long long,int> > q;
int n,m;
long long s[300010];
long long ans=0xfffffffffffffff0;
int main(){
	freopen("maxsubseqsum.in","r",stdin);
	freopen("maxsubseqsum.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m;
	q.push_back({0,0});
	for(int i=1;i<=n;i++){
		cin>>s[i];
		s[i]+=s[i-1];
		while(!q.empty()&&i-q.front().second>m){
			q.pop_front();
		} 
		if(s[i]-q.front().first>ans){
			ans=s[i]-q.front().first;
		}
		while(!q.empty()&&q.back().first>s[i]){
			q.pop_back();
		}
		q.push_back({s[i],i});
	}
	cout<<ans<<endl;
    return 0;
}