#include <bits/stdc++.h>
using namespace std;
const int N = 2e6+9;
int n,m;
int a[N],q[N];
int main()
{
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        a[i] += a[i - 1];
    }
    deque<int>q;
    q.push_back(0);
    int ma=0;
    for (int i = 1; i <= n; i++)
    {
        while (q.front() + m < i)
            q.pop_front();

        ma = max(ma, a[i] - a[q.front()]);
        while (q.size() && a[q.back()] >= a[i])
            q.pop_back();
        q.push_back(i);
    }
    cout << ma;
    return 0;
}