N, K, X, Y = gets.split.map &:to_i
A  = gets.split.map &:to_i
A.map!{|a| (a - 1).fdiv(K).ceil }.sort!
cusum = [sum = 0] + A.map{|a| sum += a}
B = [0] + A
p (0..N).map{|i|
  Y * B[i] + X * (cusum[N] - cusum[i] - B[i] * (N - i))
}.min