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