#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define REPLL(i, n) for (ll i = 0; i < (ll)(n); i++)
using namespace std;
template<class T>inline bool chmax(T &a, const T &b){if(a < b){a = b; return 1;}return 0;}
template<class T>inline bool chmin(T &a, const T &b){if(a > b){a = b; return 1;}return 0;}
typedef long long ll;

// yukicoder No.1071 ベホマラー
// 2020.06.06
// Kの商の繰り上げ、昇順に並び替え、右側から累積和、O(N)

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  ll N, K, X, Y; cin >> N >> K >> X >> Y;
  vector<ll> A(N);
  REPLL(i, N){
    cin >> A[i]; A[i]--;
    A[i] = (A[i]+(K-1))/K;
  }
  sort(A.begin(), A.end());
  vector<ll> AA(N);
  for(ll i = N-1; i >= 0; i--){
    if(i == N-1){
      AA[i] = A[i];
    }else{
      AA[i] = AA[i+1]+A[i];
    }
  }

  ll ans = 1e18;
  ans = min(ans, A[N-1]*Y);
  REPLL(i, N){
    if(i == 0){
      ans = min(ans, AA[i]*X);
    }else{
      ans = min(ans, A[i-1]*Y + (AA[i]-A[i-1]*(N-i))*X);
    }
  }
  cout << ans << endl;
}