def class_div(a,n,m,f)
  if f then
    1.upto(n) do |i|
      a << i
    end
  else
    n.downto(1) do |i|
      a << i
    end
  end

  if a.size >= m then
    a
  elsif f then
    class_div(a,n,m,false)
  else
    class_div(a,n,m,true)
  end
end

students, classes = gets.split.map(&:to_i)
hanako, taro = gets.split.map(&:to_i)

max = hanako > taro ? hanako : taro

arr = []
arr = class_div(arr, classes, max, true)

if arr[hanako-1] == arr[taro-1] then
  puts "YES"
else
  puts "NO"
end