#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <assert.h>

using namespace std;

typedef long long ll;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define per(i,a,b) for(ll i=b-1LL;i>=(a);--i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(c) string(1,c)
#define print(x) cout<<#x<<" = "<<x<<endl;

#define MOD 1000000007

int main(){
  ll n,k,x,y;
  cin>>n>>k>>x>>y;
  assert(1<=n&&n<=100000);
  assert(1<=k&&k<=1000000000);
  assert(1<=x&&x<=1000000000);
  assert(1<=y&&y<=1000000000);
  vector<ll> v;
  v.pb(0);
  rep(i,0,n){
    ll a;
    cin>>a;
    assert(1<=a&&a<=1000000000);
    a--;
    v.pb((a+k-1)/k);
  }
  sort(all(v));
  ll ans = 0;
  rep(i,1,v.sz){
    ll d = v[i]-v[i-1];
    ans += d*min(x*(n+1-i),y);
  }
  cout << ans << endl;
  return 0;
}