import math
P = list(map(int, input().split()))
Q = list(map(int, input().split()))
x = Q[0] - P[0]
y = Q[1] - P[1]
if x < 0:
    x *= -1
if y < 0:
    y *= -1
ans = (x + y) / 2
if (x + y) % 2 == 1:
    print(ans)
else:
    ans = (x + y) / 2
    print(math.ceil(ans))