def solve x, m
    tmp = x - 1
    if tmp / m % 2 == 0
        return tmp % m + 1
    else
        return m - tmp % m 
    end
end
n, m = gets.split.map(&:to_i)
x, y = gets.split.map(&:to_i)
if solve(x, m) == solve(y, m)
    puts "YES"
else
    puts "NO"
end