N,M = list(map(int,input().split()))
X,Y = list(map(int,input().split()))
X = X % (2 * M)
Y = Y % (2 * M)
if X == 0:X = 2 * M
if Y == 0:Y = 2 * M
if X == Y or X + Y == 2 * M +1:
    print('YES')
else:
    print('NO')