# -*- coding: utf-8 -*-

gx, gy = map(int, raw_input().split())
jx, jy = map(int, raw_input().split())

naname = min(abs(gx), abs(gy))

shortest = max(abs(gx), abs(gy))

if gx == gy and jx == jy and gx > jx:
    print shortest + 1
else:
    print shortest