#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod * mod;
constexpr int MAX = 200010;

int main(){
    int n; lint K, X, Y;
    scanf("%d%lld%lld%lld", &n, &K, &X, &Y);
    lint a[n];
    rep(i, n){
        scanf("%lld", &a[i]);
        a[i] = div_ceil(a[i]-1, K);
    }
    sort(a, a+n, greater<>());
    int k = Y / X;
    if(k >= n){
        printf("%lld\n", X * accumulate(a, a+n, 0LL));
        return 0;
    }
    lint ans = Y * a[k];
    rep(i, k) ans += X * (a[i] - a[k]);
    printf("%lld\n", ans);
}