N, M = map(int, input().split())
X, Y = map(int, input().split())
X -= 1
Y -= 1

if X//M%2==0:
    A = X%M
else:
    A = M-1-X%M

if Y//M%2==0:
    B = Y%M
else:
    B = M-1-Y%M

if A==B:
    print('YES')
else:
    print('NO')