#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define repr(i,n) for(int i = (int)(n); i >= 0; i--)
#define all(v) v.begin(),v.end()
typedef long long ll;

int main(){
    ll N,K,X,Y;
    cin >> N >> K >> X >> Y;
    vector<ll> vec(N);
    rep(i,N){
        cin >> vec[i];
        vec[i]--;
    }
    sort(all(vec));
    ll ans = 0;
    ll border = Y / X;
    if (N <= border){
        rep(i,N){
            if (vec[i] % K == 0) ans += X * (vec[i] / K);
            else ans += X * (vec[i] / K + 1);
        }
    }
    else{
        ll a = vec[N - 1 - border];
        if (a % K == 0) ans += Y * (a / K);
        else ans += Y * (a / K + 1);
        ll b;
        if (a % K == 0) b = a / K;
        else b = a / K + 1;
        for (int i = N - border; i < N; i++){
            vec[i] -= b * K;
            if (vec[i] % K == 0) ans += X * (vec[i] / K);
            else ans += X * (vec[i] / K + 1);
        }
    }
    cout << ans << endl;
}