n = int(input())
a = []
g = [[] for _ in range(2 * 10**5 - 1)]
g_r = [[] for _ in range(2 * 10**5 - 1)]

for _ in range(n):
    u, v = map(int, input().split())
    a.append([u - 1, v - 1])
    g[v - 1].append(u - 1)
    g_r[u - 1].append(v - 1)

order = []
sw = [True for _ in range(2 * 10**5 - 1)]
def dfs(s):
    sw[s] = False
    for i in g[s]:
        if sw[i]:
            dfs(i)
    order.append(s)
dfs(v - 1)

order_R = []
sw = [True for _ in range(2 * 10**5 - 1)]
def dfs(s):
    sw[s] = False
    for i in g[s]:
        if sw[i]:
            dfs(i)
    order_R.append(s)
dfs(order[len(order) - 1])

if len(order_R) != n:
    print(0)
else:
    count = 0
    z = set()
    x = order_R[0]
    y = order_R[-1]
    for i in range(len(order_R) - 1):
        if order_R[i] == y and order_R[i + 1] == x:
            count += 1
        z.add(order_R[i])
    z.add(y)
    
    if count < a.count([y, x]):
        print(len(z))
    else:
        print(1)