#include <algorithm>
#include <cstring>
#include <iostream>
#include <map>
#include <set>
#include <vector>
using namespace std;
#define int long long
typedef pair<int, int> PII;
const int N = 1e5 + 10;
int t, n, m;
int a[N], s[N];
map<int, int> mp1;
signed main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    for (int i = 1; i <= n; i++)
    {
        s[i] = s[i - 1] + a[i];
    }
    int minv = 1e9;
    int ans = -1e9;
    for (int i = m; i <= n; i++)
    {
        minv = min(minv, s[i - m]);
        ans = max(ans, s[i] - minv);
    }
    cout << ans << endl;
    return 0;
}