def read_data():
    x, y = map(int, input().split())
    x2, y2 = map(int, input().split())
    return x, y, x2, y2

def solve(x, y, x2, y2):
    d = max(abs(x), abs(y))
    if x == y and x2 == y2 and x * x2 > 0 and abs(x) > abs(x2):
        d += 1
    elif x == -y and x2 == -y2 and x * x2 > 0 and abs(x) > abs (x2):
        d += 1
    return d

x, y, x2, y2 = read_data()
print(solve(x, y, x2, y2))