n, m, p, q = gets.split.map(&:to_i)
(1..Float::INFINITY).each do |i|
  x = (i - 1) % 12 + 1
  if p <= x && x <= p + q - 1
    n -= 2 * m
  else
    n -= m
  end
  if n <= 0
    puts i
    break
  end
end