x,y = map(int,raw_input().split(" "))
x2,y2 = map(int,raw_input().split(" "))
if x == x2 == 0 or y == y2 == 0:
	print x + y
else:
	if (0 < x2 < x or x < x2 < 0) and (0 < y2 < y or y < y2 < 0):
		if abs(x) == abs(y) and abs(x2) == abs(y2):
			print abs(x) + 1
		else:
			print abs(x)
	else:
		print max(abs(x),abs(y))