n = int(input())

v = set()
z = {}
for _ in range(n):
    x, y = map(int, input().split())
    if x in v:
        z[x] += 1
    else:
        v.add(x)
        z[x] = 1
    if y in v:
        z[y] -= 1
    else:
        v.add(y)
        z[y] = -1

count_p1 = 0
count_0 = 0
count_m1 = 0

for i in v:
    if z[i] == 0:
        count_0 += 1
    elif z[i] == 1:
        count_p1 += 1
    elif z[i] == -1:
        count_m1 += 1

if count_m1 == 1 and count_p1 == 1 and count_0 == len(v) - 2:
    print(1)
elif count_0 == len(v):
    print(len(v))
else:
    print(0)