# https://yukicoder.me/problems/no/396


def select_class(class_M, rank):
    ans = rank % (2 * class_M)
    if ans == 0:
        return 1
    elif ans > class_M:
        return ans - (2 * (ans - class_M) - 1)
    else:
        return ans


def main():
    _, M = map(int, input().split())
    X, Y = map(int, input().split())
    print(['NO', 'YES'][select_class(M, X) == select_class(M, Y)])


main()