from sys import stdin, stdout

input = lambda: stdin.readline().rstrip()
write = stdout.write

def main():
    N, M = map(int, input().split())
    X, Y = map(int, input().split())

    class_ = [0, 0]
    for i, n in enumerate((X, Y)):
        div_, mod_ = divmod(n - 1, M)
        if div_ % 2:
            class_[i] = M - mod_
        else:
            class_[i] = mod_ + 1

    if class_[0] == class_[1]:
        write('YES\n')
    else:
        write('NO\n')

main()