#include<bits/stdc++.h>
using namespace std;

#define int long long
int n,m,ans,val,p[500005];
queue<int> q;

signed main()
{
	cin>>n>>m;
	for(int i = 1;i<=n;i++) cin>>p[i];
	ans = -1e18;
	for(int i = 1;i<=n;i++){
		while(!q.empty()){
			int x = q.front();
			if(val>0&&i-x+1<=m) break;
			val -= p[x];
			q.pop();
			ans = max(ans,val);
		}
		q.push(i);
		val += p[i];
		ans = max(ans,val);
	}
	cout<<ans;
	return 0;
}