def ask(x):
	q,r = divmod(x,M)
	if r == 0:
		return M if q%2 else 1
	return M+1-r if q%2 else r
N,M = map(int,raw_input().split())
X,Y = map(int,raw_input().split())
print "YES" if ask(X) == ask(Y) else "NO"