x, y = map(int, raw_input().split())
x2, y2 = map(int, raw_input().split())

ans = max(abs(x), abs(y))
if abs(x) == abs(y) and abs(x2) == abs(y2):
    if (0 < x2 < x or x < x2 < 0) and (0 < y2 < y or y < y2 < 0):
        ans += 1
print ans