n, m = gets.split().map(&:to_i)
x, y = gets.split().map(&:to_i)

x = (x-1) % (2*m)
y = (y-1) % (2*m)

x = m-1-(x%m) if m<=x
y = m-1-(y%m) if m<=y

puts (x==y)? 'YES': 'NO'