#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<map>
#include<cmath>
#include<queue>
#include<stack>
#include<list>

#define endl "\n"
using namespace std;
using ll = long long;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define REP(i, n) for(int i = 0; i < n; i++)
using Graph = vector<vector<int>>;

int main(){
    ll n,k,x,y;
    cin>>n>>k>>x>>y;
    vector<ll> a(n);
    for(ll i=0;i<n;i++){
        cin>>a[i];
    }
    sort(a.begin(),a.end());

    if(a[n-1] == 1){
        cout<<0<<endl;
        return 0;
    }

    ll ans = 0;
    ll tmp = 0;
    for(ll i=0;i<n;i++){
        if(a[i] == 1){
            tmp++;
        }
    }
    for(ll i=0;i<(a[n-1]-1+k-1)/k;i++){
        ans += min( (n-tmp)*x, y);
        while(i == (a[tmp]-1+k-1)/k-1){
            tmp++;
        }
        // cout<<ans<<" "<<n-tmp<<endl;
    }

    cout<<ans<<endl;
}