#include <bits/stdc++.h>


int main(){
  int64_t N, K, X, Y;

  while(std::cin >> N >> K >> X >> Y){
    std::vector<int64_t> A(N);
    for(int i = 0; i < N; ++i) std::cin >> A[i];

    std::sort(A.begin(), A.end());
    for(int i = 0; i < N; ++i){
      A[i] -= 1;
      A[i] = (A[i] + K - 1) / K;
    }

    int64_t ans = 0;

    int64_t t = 0;
    for(int i = 0; i < N; ++i){
      ans += std::min((A[i] - t) * (N - i) * X, (A[i] - t) * Y);
      t = A[i];
    }


    

    std::cout << ans << "\n";
  }
  

  return 0;
}