#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  ll N, K, X, Y;
  cin >> N >> K >> X >> Y;

  vector<ll> v;
  rep(i,N){
    ll a;
    cin >> a;
    ll x = (a-1+(K-1))/K;
    v.push_back(x);
  }
  sort(ALLOF(v));

  ll x = 0;
  rep(i,N+1){
    if(X*i<Y){
      x = i;
    }
  }
  ll y = -1;
  
  if(x == N){
    y = 0;
  }else{
    y = v[N-1-x];
  }

  ll ret = y * Y;
  rep(i,N){
    ll z = max(0LL, v[i]-y);
    ret += z * X;
  }

  cout << ret << endl;
  
  return 0;
}