#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, k, x, y; cin >> n >> k >> x >> y;
  chmin(x, y);
  vector<int> a(n); REP(i, n) cin >> a[i], --a[i];
  sort(ALL(a));
  ll ans = 0;
  REP(i, n) ans += 1LL * (a[i] + k - 1) / k * x;
  if (n == 1 || (a[n - 2] + k - 1) / k == (a[n - 1] + k - 1) / k) {
    chmin(ans, 1LL * (a[n - 1] + k - 1) / k * y);
  } else {
    int tmp = (a[n - 2] + k - 1) / k;
    // cout << tmp << '\n';
    chmin(ans, 1LL * tmp * y + 1LL * (a[n - 1] - tmp * k + k - 1) / k * x);
  }
  cout << ans << '\n';
  return 0;
}