from collections import Counter
n, k, x, y = map(int, input().split())
A = list(map(int, input().split()))
c = Counter()
tot = 0
for a in A:
	c[(a-2)//k+1] += 1
	tot += (a-2)//k+1

ans = tot * x
l = sorted(list(c.items()))

tmp_key = 0
tmp_val = n
for i in range(len(l)):
	key, val = l[i]
	tot -= (key-tmp_key) * tmp_val
	tmp_val -= val
	tmp_key = key
	ans = min(ans, tot * x + key * y)

print(ans)