#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef long long ll;
ll N, K, X, Y;
int A[100000];

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    cin >> N >> K >> X >> Y;
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        A[i]--;
    }
    sort(A, A+N);
    ll ans = 0;
    ll tmp = 0;
    for(int i = 0; i < N; i++){
        ll m = N-i;
        ll nx = ((A[i]+K-1)/K)*K;
        ll cnt = (nx-tmp)/K;
        if(tmp >= A[i]) continue;
        if(m*X < Y){
            ans += m*X*cnt;
        }else{
            ans += Y*cnt;
        }
        tmp = nx;
    }
    cout << ans << endl;
}