#include<bits/stdc++.h> 
using namespace std;
typedef long long ll;
template<typename T1,typename T2> bool chmin(T1 &a,T2 b){if(a<=b)return 0; a=b; return 1;}
template<typename T1,typename T2> bool chmax(T1 &a,T2 b){if(a>=b)return 0; a=b; return 1;}
int dx[4]={0,1,0,-1}, dy[4]={1,0,-1,0};
long double eps = 1e-9;
long double pi = acos(-1);



signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);

    
    
    ll n,k,x,y;
    cin>>n>>k>>x>>y;
    ll a[n];
    ll ans = 0;
    for(int i=0;i<n;i++){
        cin>>a[i];
        a[i]--;
        ans += (a[i] + k-1) / k * x;
    }
    sort(a,a+n);
    ll sum[n+1]={};
    for(int i=n-1;i>=0;i--){
        sum[i] = sum[i+1] + (a[i]+k-1)/k*x; 
    }
    for(int i=0;i<n;i++){
        ll cnt = a[i]/k + (a[i]%k!=0);
        ll ret = sum[i+1] + cnt*y;
        ret -= x*cnt*(n-i-1);
        chmin(ans,ret);
    }
    cout << ans << endl;

}