#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;
constexpr int INF = 2e9;

int main() {
  int n;
  ll k, x, y;
  cin >> n >> k >> x >> y;
  vector<ll> a(n);
  rep(i,n) cin >> a[i], a[i]--;
  ll lim = 0;
  a.emplace_back(0);
  for (int i = 1; i <= n; i++) {
    if (x * i < y) lim = i;
  }
  sort(a.begin(), a.end(), greater<ll>());

  ll cnt = (a[lim] + k - 1) / k;
  ll res = cnt * y;
 
  for (int i = 0; i < lim; i++) {
    a[i] -= cnt * k;
    a[i] = max(0LL, a[i]);
    res += x * ((a[i] + k - 1) / k);
  }
  cout << res << endl;
  return 0;
}