x1, y1, x2, y2 = map(int, input().split())

b = (x1, y1)
house_ = [
    (x2-2, y2-1), (x2-2, y2+1),
    (x2-1, y2-2), (x2-1, y2+2),
    (x2+1, y2-2), (x2+1, y2+2),
    (x2+2, y2-1), (x2+2, y2+1),
    (x2, y2)
]

way = [(0, 0)]

n = 0
for i in way:

    if i == b:
        n += 1
        continue

    if i[0] > b[0] or i[1] > b[1]:
        continue

    if i in house_:
        continue

    way.append((i[0]+1, i[1]))
    way.append((i[0], i[1]+1))

# print(way)
print(n)

只过了前两个，求求了