# 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():
    N, M = map(int, input().split())
    X, Y = map(int, input().split())
    hanako = select_class(M, X)
    taro = select_class(M, Y)
    if hanako == taro:
        print("YES")
    else:
        print("NO")


main()