# UnionFind 参考は以下のサイト
# https://note.nkmk.me/python-union-find/
from collections import defaultdict

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        group_members = defaultdict(list)
        for member in range(self.n):
            group_members[self.find(member)].append(member)
        return group_members

    def __str__(self):
        return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())


N = int(input())
uf = UnionFind(2*10**5+1)
USE = [0]*(2*10**5+1)
L = [0]*(2*10**5+1)
for i in range(N):
    h,w = map(int, input().split())
    uf.union(h,w)
    USE[h],USE[w]=1,1
    L[h]+=1
    L[w]-=1
root = uf.find(h)
useCnt = sum(USE)
if uf.size(root)==useCnt:
    u = 0
    d = 0
    for i in range(len(L)):
        if abs(L[i])>1:
            print(0)
            exit()
        if L[i]==1:
            u+=1
        if L[i]==-1:
            d+=1
    if u==1 and d==1:
        print(1)
    elif u==0 and d==0:        
        print(useCnt)
    else:
        print(0)
else:
    print(0)