n = list(map(int,input().split()))
x = list(map(int,input().split()))

def cla(x, i=0, j=0):
	while i < x:
		i = i + n[1]
		j = j+1
	j = j%2
	if j == 1:
		return(x%n[1])
	else:
		return((n[1]-x%n[1]+1)%4)
if cla(x[0]) == cla(x[1]):
	print('YES')
else:
	print('NO')