#include "iostream"
#include "vector"
using namespace std;
int main() {
int n;
cin >> n;
vector<int> arr(n);
for (int i = 0; i < n; i++) {
cin >> arr[i];
}
int with;
cin >> with;
// cout << n << endl;
// for (int i = 0; i < n; i++) {
// cout << arr[i];
// }
// cout << "" << endl;
// cout << with << endl;
int sum = 0;
int ans = 0;
for (int i = 0; i < with; i++) {
sum += arr[i];
}
ans = sum;
int right = with;
for (;right < n;right++) {
sum = sum + arr[right] - arr[right-with];
ans = max(ans, sum);
}
cout << ans << endl;
return 0;
}