#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	int k = ri();
	int x = ri();
	int y = ri();
	int a[n + 1];
	for (int i = 0; i < n; i++) {
		int x = ri() - 1;
		a[i] = x ? (x - 1) / k + 1 : x;
	}
	a[n] = 0;
	std::sort(a, a + n, std::greater<>());
	int64_t cost0 = 0;
	int64_t res = 1000000000000000000;
	for (int i = 0; i <= n; i++) {
		if (cost0 > 1000000000) continue;
		res = std::min(res, (int64_t) x * cost0 + (int64_t) y * a[i]);
		if (i < n) cost0 += (int64_t) (a[i] - a[i + 1]) * (i + 1);
	}
	printf("%" PRId64 "\n", res);
	return 0;
}