N,M = map(int,input().split())
X,Y = map(int,input().split())
X,Y = X - 1,Y - 1
if N <= M:
	print('NO')
elif X // M % 2 == 0 and Y // M % 2 == 0:
	if X % M == Y % M:
		print('YES')
	else:
		print('NO')
elif X // M % 2 == 0 and Y // M % 2 == 1:
	if X % M == M - 1 - (Y % M):
		print('YES')
	else:
		print('NO')
elif X // M % 2 == 1 and Y // M % 2 == 0:
	if M - 1 - (X % M) == Y % M:
		print('YES')
	else:
		print('NO')