import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

x, y = MI()
a, b = MI()

if a == 0 and x == 0:
    if b*y < 0 or abs(b) > abs(y):
        print(abs(y))
    else:
        print(abs(y))
elif b == 0 and y == 0:
    if a*x < 0 or abs(a) > abs(x):
        print(abs(x))
    else:
        print(abs(x))
elif abs(x) == abs(y) and abs(a) == abs(b):
    if x * a > 0 and y * b > 0 and abs(x) > abs(a) and abs(y) > abs(b):
        print(abs(x)+2)
    else:
        print(abs(x))
else:
    print(max(abs(x), abs(y)))