#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define vi vector<int>
#define vvi vector<vector<int>>
#define all(a) (a).begin(), (a).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
const int MOD = 1e9+7;
const ll LINF = 1e18;
const int INF = 1e9;
ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S, T;

int main()
{

    cin >> N >> K >> X >> Y;
    vi arr(N);
    vi brr;
    for (int i = 0; i < N; i++) {cin >> A;arr.at(i) =A-1;}

    rep(i,N)
    {
        if(arr[i] > 0)
        {
            brr.push_back(arr[i]);
        }
    }
    
    while(!brr.empty())
    {
        B = brr.size();
        vi crr;

        C += min(B*X,Y);
        rep(i,B)
        {
            brr[i] -= K;
            if(brr[i] > 0) crr.push_back(brr[i]);
        }
        brr = crr;
        crr.clear();
    }

    cout << C;


    return 0;
}