N, K, X, Y = gets.split.map(&:to_i)
A = gets.split.map { |a| a.to_i - 1 }.sort
C = A.map { |a| a / K + (a % K == 0 ? 0 : 1) }

if X >= Y
  puts C.max
  exit
end

if N * X <= Y
  puts C.map { |c| c * X }.sum
  exit
end

ok = Y / X

bhm_cnt = ok == N ? 0 : C[N - ok - 1]
bh_cnt = C[N - ok..].map { |c| c - bhm_cnt }.sum

# p [:bh_cnt, bh_cnt, :bhm_cnt, bhm_cnt]
puts X * bh_cnt + Y * bhm_cnt