fi = open('paint.in', 'r')
fo = open('paint.out', 'w')

a, b = map(int, fi.readline().split())
c, d = map(int, fi.readline().split())

len = max(b, d) - min(c, a)
if a < c and b < c:
    len -= c - b
elif c < a and d < a:
    len -= d - a

print(len, file = fo)