#-------------------------------------------------------------------
import sys
def p(*_a):
  _s=" ".join(map(str,_a))
  #print(_s)
  sys.stderr.write(_s+"\n")
#-------------------------------------------------------------------
import math

N,K,X,Y = map(int, input().split())
A = list(map(int, input().split()))

maxA = max(A)

if maxA==1:
  print(0)
  exit()


B = sorted(A)

# 回数、逆順、累積和
C=[0]*N
for i in range(N)[::-1]:
  C[i] = math.ceil( (B[i]-1) / K )
  if i < N-1: C[i] += C[i+1]

#p("C = ",C)

hp = 1
i = 0
ans = 0
while i<N:
  a = A[i]
  if a <= hp:
    i += 1
    continue

  if C[i]*X >= (math.ceil(maxA/K))*Y:
    hp += K
    ans += Y
  else:
    A[i] -= K
    ans += X

print(ans)