#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;
}