#include <cstdio>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <iterator>
#include <cassert>
#include <numeric>
#include <functional>
//#include <numeric>
#pragma warning(disable:4996) 
 
typedef long long ll;
typedef unsigned long long ull;
#define MIN(a, b) ((a)>(b)? (b): (a))
#define MAX(a, b) ((a)<(b)? (b): (a))
#define LINF  9223300000000000000
#define LINF2 1223300000000000000
#define LINF3 1000000000000
#define INF 2140000000
const long long MOD = 1000000007;
//const long long MOD = 998244353;

using namespace std;


void solve()
{
    int n, K, x, y;
    scanf("%d%d%d%d", &n, &K, &x, &y);

    int m=y / x;

    vector<int> a(n);
    int i;
    for (i = 0; i < n; i++) {
        int tmp;
        scanf("%d", &tmp);
        int tmp2=(tmp - 1) / K;
        if ((tmp - 1) % K) tmp2++;
        a[i] = tmp2;
    }
    sort(a.rbegin(), a.rend());

    vector<ll> s(n + 1);
    for (i = 0; i < n; i++) {
        s[i + 1] = s[i] + a[i];
    }

    ll ans = s[n] * x;
    for (i = 0; i < n; i++) {
        ll ans0 = (s[i + 1] - (ll)(i+1)*a[i])*(ll)x;
        ans0 += (ll)y*a[i];
        ans = MIN(ans, ans0);
    }
    printf("%lld\n", ans);

    return;
}


int main(int argc, char* argv[])
{
#if 1
    solve();
#else
    int T;
    scanf("%d", &T);
    int t;
    for(t=0; t<T; t++) {
        //printf("Case #%d: ", t+1);
        solve();
    }
#endif
    return 0;
}