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

deque < int > dq;
int a[500005]; 

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
		cin >> a[i];
	int sum = 0, ans = INT_MIN;
	for (int i = 1; i <= n; i++)
	{
		dq.push_back(a[i]);
		while (dq.size() > m)
		{
			sum -= a[i - dq.size() + 1];
			dq.pop_front();
		}
		sum += a[i];
		ans = max(sum, ans);
		while (sum < 0)
		{
			sum -= a[i - dq.size() + 1];
			dq.pop_front();
		}
	}
	cout << ans << '\n';
	return 0;
}