#include <bits/stdc++.h>

using namespace std;

using ll = long long;
#define endl '\n'

const int N = 2e5 + 10;

int n, p;
ll sum[N], a[N], k, t;

void solve() {
    cin >> n >> p;
    for (int i = 1; i <= n; i ++) {
        cin >> a[i];
        sum[i] = a[i] + sum[i - 1];
    }
    cin >> k >> t;
    ll ans = 0;
    for (int i = 1; i <= n; i ++) {
//      cout << i << " *************\n";
        if (i <= p) {
            if (p - i + 1 > t) continue;
            if (t - (p - i + 1) + i <= n) {
                int r = t - (p - i + 1) + i;
                ll now;
                if (r <= p) {
                    now = sum[p] - sum[i - 1];
                    now += k * t * (p - i + 1) - k * (p - i) * (p - i + 1) / 2;
                } else {
                    now = sum[r] - sum[i - 1];
                    now += k * t * (r - i + 1) - k * (r - i) * (r - i + 1) / 2;
                }
//              cout << "debug1: " << now << endl;
                ans = max(ans, now);
                continue;
            }
            ll now = sum[n] - sum[i - 1];
            now += k * t * (n - i + 1) - k * (n - i) * (n - i + 1) / 2;
            ans = max(ans, now);
//          cout << "1: " << now << endl;
        } else {
            if (i - p + 1 > t) continue;
            if (t - (i - p + 1) < i) {
                int l = i - (t - (i - p + 1));
                ll now;
                if (l >= p) {
                    now = sum[i] - sum[p - 1];
                    now += k * t * (i - p + 1) - k * (i - p) * (i - p + 1) / 2;
                } else {
                    now = sum[i] - sum[l - 1];
                    now += k * t * (i - l + 1) - k * (i - l) * (i - l + 1) / 2;
                }
//              cout << "debug2: " << now << endl;
                ans = max(ans, now);
                continue;
            }
            ll now = sum[i] + k * t * i - k * (i - 1) * i / 2;
            ans = max(ans, now);
//          cout << "2: " << now << endl;
        }
    }
    cout << ans << endl;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int _ = 1;
    cin >> _;
    while (_--)
        solve();
    return 0;
}