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


def f(x, m):
    q, r = divmod(x - 1, m)
    if q % 2:
        return m - r - 1
    else:
        return r


if f(X, M) == f(Y, M):
    print('YES')
else:
    print('NO')