#pragma region
#pragma GCC target("avx2")
#pragma GCC optimize("03")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std; typedef long double ld; typedef long long ll;
typedef unsigned long long ull;
#define endl "\n"
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define VPII vector<PII>
#define VPLL vector<PLL>
#define ALL(x) (x).begin(), (x).end()
constexpr int INF=1<<30; constexpr ll LINF=1LL<<60; constexpr ll mod=1e9+7; constexpr int NIL = -1;
template<class T>inline bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>inline bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
#pragma endregion
//-------------------
const int MX = 1e5+3;
ll a[MX];

int main(){
    cin.tie(0); ios::sync_with_stdio(false); //cout << fixed << setprecision(15);
    ll n,k,x,y; cin >> n >> k >> x >> y;
    FOR(i,0,n-1) {
        cin >> a[i];
        a[i]--;
    }

    ll ans = 0;
    // if(x * n <= y) {
    //     FOR(i,1,n) ans += (a[i]-1+k-1)/k;
    // } else {

    // }
    ll mx = y / x;
    // cout << mx << endl;
    sort(a, a+n);
    if(mx >= n) {
        FOR(i,0,n-1) ans += (a[i]+k-1)/k;
        cout << ans << endl;
        return 0; 
    }
    ll cnt_y = (a[n-1-mx]+k-1)/k;
    // cout << cnt_y << endl;
    ans += cnt_y * y;
    for(int i=n-1; i>=n-mx; i--) {
        ll cur = a[i]-cnt_y*k;
        ans += (cur >= 0)? (cur+k-1)/k * x:0LL;
    }

    cout << ans << endl;
    return 0;
}