#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
#define DUMP(x) cout << #x << " = " << (x) << endl;
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define IFOR(i, m, n) for (ll i = n - 1; i >= m; i--)
#define REP(i, n) FOR(i, 0, n)
#define IREP(i, n) IFOR(i, 0, n)
#define FOREACH(x, a) for (auto&(x) : (a))
#define ALL(v) (v).begin(), (v).end()
#define SZ(x) ll(x.size())

int main() {
  ll n, k, x, y;
  cin >> n >> k >> x >> y;
  vector<ll> a(n);
  REP(i, n) {
    cin >> a[i];
    a[i]--;
  }
  sort(ALL(a));

  if (x >= y) {
    cout << y * ((a[n - 1] + k - 1) / k) << endl;
    return 0;
  }

  ll t = (y + x - 1) / x;

  // floor(a[j]/k) >=i となるjがt個以上となるiのmaxを見つける
  ll ok = 0, ng = 1e18;
  while (ok + 1 < ng) {
    ll m = (ok + ng) / 2;
    ll cnt = 0;
    REP(i, n) {
      if (m <= (a[i] + k - 1) / k) {
        cnt++;
      }
    }
    (cnt >= t ? ok : ng) = m;
  }

  ll sum = 0;
  REP(i, n) { sum += max(0LL, -ok + ((a[i] + k - 1) / k)); }
  cout << y * ok + x * sum << endl;
}