#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N, K, X, Y;
	cin >> N >> K >> X >> Y;
	vector<int> A(N);
	REP(i, N) {
		scanf("%d", &A[i]);
		A[i] = (A[i] - 1 + K - 1) / K;
	}
	sort(ALL(A));
	vector<ll> sum(N + 1);
	REP(i, N) sum[i + 1] += sum[i] + A[i];
	ll ans = sum[N] <= longINF / X ? sum[N] * X : longINF;
	REP(i, N) {
		// 人 i まで全体魔法
		ll cur = (ll)A[i] * Y;
		// 残り s 回個別魔法
		ll s = (sum[N] - sum[i + 1]) - (ll)(N - i - 1) * A[i];
		
		if (s <= longINF / X) chmin(ans, cur + s * X);
	}
	cout << ans << endl;
}