Lesson7

#include <iostream>
#include <vector>

using namespace std;
using ll=long long;

void Solve() {
  int n; cin >> n;
  vector<int> a(n);
  for (auto& x : a) cin >> x;
  int k; cin >> k;
  ll mx = INT_MIN;
  ll sm = 0;
  for (int i = 0; i < k; ++i) sm += a[i];
  for (int i = 0; i <= n - k; ++i) {
    mx = max(mx, sm);
    if (i < n - k) sm += a[i + k] - a[i];
  }
  cout << mx << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);

  Solve();
  return 0;
}