n, m = map(int, input().split())
x, y = map(int, input().split())

def cl(k):
    r = (k - 1) % (2 * m)
    if r < m:
        return r
    else:
        return 2 * m - 1 - r

if cl(x) == cl(y):
    print('YES')
else:
    print('NO')