# -*- coding: utf-8 -*-
X, Y = map(int, raw_input().split())
x, y = map(int, raw_input().split())
delX = abs(X)
delY = abs(Y)
if delY == delX:
    step = delX
    if x == y and X - x > 0:
        step += 1
else:
    step = max(delX, delY)
print step