# frozen_string_literal: true

A, B, C, D, E = gets.split.map { _1.to_i }

def solve
  result = 0
  price = D

  (1..((B - C) * A)).each do |i|
    price -= E if (i % 10).zero? && (price >= E)

    result += price
  end

  result
end

puts solve