#coding=UTF-8

mojir=input()
hyo=mojir.split(' ')
x=int(hyo[0])
y=int(hyo[1])

mojir=input()
hyo=mojir.split(' ')
x2=int(hyo[0])
y2=int(hyo[1])

ans=max(abs(x),abs(y))
if abs(x)==abs(y) and abs(x2)==abs(y2):
    if (x//abs(x),y//abs(y)) == (x2//abs(x2),y2//abs(y2)):
        ans=ans+1#避ける必要がある

print(ans)