#include <iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<math.h>
using namespace std;
typedef long long ll;
#define int long long
#define double long double
typedef vector<int> VI;
typedef pair<int, int> pii;
typedef vector<pii> VP;
typedef vector<string> VS;
typedef priority_queue<int> PQ;
template<class T>bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }
#define fore(i,a) for(auto &i:a)
#define REP(i,n) for(int i=0;i<n;i++)
#define eREP(i,n) for(int i=0;i<=n;i++)
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define eFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define SORT(c) sort((c).begin(),(c).end())
#define rSORT(c) sort((c).rbegin(),(c).rend())
#define LB(x,a) lower_bound((x).begin(),(x).end(),(a))
#define UB(x,a) upper_bound((x).begin(),(x).end(),(a))
#define INF 1000000000
#define LLINF 9223372036854775807
#define mod 1000000007
#define eps 1e-12 
//priority_queue<int,vector<int>, greater<int> > q2;
int N, K, X, Y;
VI A;

int check(int M) {
	//cout << M << endl;
	int res = Y * M;
	VI tmp = A;
	
	REP(i, N) {
		//cout << A[i] << " ";
		tmp[i] -= M * K;
		if (tmp[i] > 0)res += ((tmp[i] + K - 1) / K) * X;
	}
	//cout << M << " " << res << endl;
	//cout << endl;

	return res;
}

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	
	cin >> N >> K >> X >> Y;
	A.resize(N);
	REP(i, N) {
		cin >> A[i];
		A[i]--;
	}

	int L = 0, R = INF + 10;
	while (R - L > 2) {
		//cout << L << " " << R << endl;
		int t1 = (L * 2 + R) / 3;
		int t2 = (L + R * 2) / 3;
		if (check(t1) < check(t2)) R = t2;
		else L = t1;
	}
	int ans = LLINF;
	//L = max(0LL, L - 5);
	//R += 5;
	//FOR(i, L, R)chmin(ans, check(i));
	cout << min({ check(L),check(L + 1), check(R) }) << endl;
	//cout << ans << endl;
	return 0;
}