#include <bits/stdc++.h>

using namespace std;

using ll = long long;

template <typename T> void range_increment(vector<T> &d, int i, int j, int n) {
  if (i > j) {
    range_increment(d, i, n - 1, n);
    range_increment(d, 0, j, n);
    return;
  }
  d[i] += 1;
  d[j + 1] -= 1;
};

static constexpr ll root = 62;
static constexpr ll M0 = 998244353;
static constexpr ll M1 = 1004535809;

ll modpow(ll b, ll e, ll mod) {
  ll ans = 1;
  for (; e; b = b * b % mod, e /= 2)
    if (e & 1)
      ans = ans * b % mod;
  return ans;
}

template <ll mod> void ntt(vector<ll> &a) {
  int n = int(a.size()), L = 31 - __builtin_clz(n);
  static vector<ll> rt(2, 1);
  for (static int k = 2, s = 2; k < n; k *= 2, s++) {
    rt.resize(n);
    ll z[] = {1, modpow(root, mod >> s, mod)};
    for (int i = k; i < 2 * k; i++)
      rt[i] = rt[i / 2] * z[i & 1] % mod;
  }
  vector<int> rev(n);
  for (int i = 0; i < n; i++)
    rev[i] = (rev[i / 2] | (i & 1) << L) / 2;
  for (int i = 0; i < n; i++)
    if (i < rev[i])
      swap(a[i], a[rev[i]]);
  for (int k = 1; k < n; k *= 2)
    for (int i = 0; i < n; i += 2 * k)
      for (int j = 0; j < k; j++) {
        ll z = rt[j + k] * a[i + j + k] % mod, &ai = a[i + j];
        a[i + j + k] = ai - z + (z > ai ? mod : 0);
        ai += (ai + z >= mod ? z - mod : z);
      }
}

template <ll mod> vector<ll> conv(const vector<ll> &a, const vector<ll> &b) {
  if (a.empty() || b.empty())
    return {};
  int s = int(a.size()) + int(b.size()) - 1, B = 32 - __builtin_clz(s),
      n = 1 << B;
  int inv = modpow(n, mod - 2, mod);
  vector<ll> L(a), R(b), out(n);
  L.resize(n), R.resize(n);
  ntt<mod>(L), ntt<mod>(R);
  for (int i = 0; i < n; i++)
    out[-i & (n - 1)] = (ll)L[i] * R[i] % mod * inv % mod;
  ntt<mod>(out);
  return {out.begin(), out.begin() + s};
}

ll euclid(ll a, ll b, ll &x, ll &y) {
  if (!b)
    return x = 1, y = 0, a;
  ll d = euclid(b, a % b, y, x);
  return y -= a / b * x, d;
}

ll crt(ll a, ll m, ll b, ll n) {
  if (n > m)
    swap(a, b), swap(m, n);
  ll x, y, g = euclid(m, n, x, y);
  assert((a - b) % g == 0); // else no solution
  x = (b - a) % n * x % n / g * m + a;
  return x < 0 ? x + m * n / g : x;
}

int main() {
  int n, k, p, q;
  cin >> n >> k >> p >> q;
  vector<ll> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int mn = *min_element(a.begin(), a.end());
  if (mn < 0) {
    mn = -mn;
    for (int i = 0; i < n; i++) {
      a[i] += mn;
    }
  } else {
    mn = 0;
  }
  vector<ll> multiplier(n + 1);
  for (int i = 0; i < p; i++) {
    ll from = (k * 1ll * i) % n;
    int to = (from + q - 1) % n;
    range_increment(multiplier, from, to, n);
  }
  partial_sum(multiplier.begin(), multiplier.end(), multiplier.begin());
  multiplier.pop_back();

  vector<int> marked(n + 1);
  for (int i = 0; i <= n - p; i++) {
    ll from = (k * 1ll * i) % n;
    int to = (from + n - q) % n;
    range_increment(marked, from, to, n);
  }
  partial_sum(marked.begin(), marked.end(), marked.begin());

  reverse(multiplier.begin(), multiplier.end());
  for (int i = 0; i < n; i++) {
    multiplier.push_back(0);
    a.push_back(a[i]);
  }

  auto c0 = conv<M0>(multiplier, a);
  auto c1 = conv<M1>(multiplier, a);

  ll ret = -1e18;
  for (int i = 0; i < n; i++) {
    if (marked[i]) {
      ll sol =
          crt(c0[i + n - 1], M0, c1[i + n - 1], M1) - mn * 1ll * p * 1ll * q;
      ret = max(ret, sol);
    }
  }
  cout << ret << '\n';
}