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