n, m = map(int, input().split())
x, y = map(int, input().split())
x, y = x-1, y-1
q1, r1 = divmod(x, m)
q2, r2 = divmod(y, m)
if q1%2 == q2%2:
    if r1 == r2:
        print('YES')
    else:
        print('NO')
else:
    if r1 == m-1-r2:
        print('YES')
    else:
        print('NO')