#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

int main(){
  int n, k, x, y;
  cin >> n >> k >> x >> y;
  vector<int> a(n);
  map<int, int> c;
  ll csum = 0;
  rep(i, n){
    int in;
    cin >> in;
    in--;
    a.at(i) = in;
    c[(in+k-1)/k]++;
    csum += (ll)(in+k-1)/k;
  }
  ll ans = 1e18+5e17;
  ll ux = 0, xc = 0;
  bool f = false;
  rrepit(ritr, c){
    ll add = (ll)ritr->first * y;
    add += (ll)ux * x;
    if(ans > add){
      ans = add;
    }else{
      f = true;
      break;
    }
    // cerr << ritr->first << " " << ritr->second << " " << ux << " " << add << endl;
    if(ritr != c.rend()){
      auto itr = ritr;
      itr++;
      ll diff = ritr->first - itr->first;
      ux += diff*(ritr->second);
      ux += diff*xc;
      xc += ritr->second;
    }
  }
  if(f == false){
    ll add = (ll)x * csum;
    ans = min(ans, add);
  }
  cout << ans << endl;

  return 0;
}