#include <bits/stdc++.h>
using namespace std;
int INF = 1000000001;
long long INF2 = 1000000000000000000;
long long f(vector<int> &A, long long X, long long Y, long long v){
  int N = A.size();
  long long ans = v * Y;
  for (int i = 0; i < N; i++){
    if (A[i] > v){
      ans += (A[i] - v) * X;
    }
  }
  return ans;
}
int main(){
  long long N, K, X, Y;
  cin >> N >> K >> X >> Y;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
    A[i] -= 1;
    A[i] = (A[i] + K - 1) / K;
  }
  sort(A.begin(), A.end());
  Y = min(Y, N * X);
  long long left = -1;
  long long right = INF;
  while (right - left > 2){
    long long mid1 = (left * 2 + right) / 3;
    long long mid2 = (left + right * 2) / 3;
    if (f(A, X, Y, mid1) > f(A, X, Y, mid2)){
      left = mid1;
    } else {
      right = mid2;
    }
  }
  long long a = f(A, X, Y, left);
  if (left == -1){
    a = INF2;
  }
  long long b = f(A, X, Y, left + 1);
  long long c = f(A, X, Y, left + 2);
  cout << min({a, b, c}) << endl;
}