import sys
import math
from collections import deque,Counter
#sys.setrecursionlimit(10**7)
int1=lambda x: int(x)-1

inp=lambda :int(input())
mi=lambda :map(int,input().split())
li=lambda :list(mi())
mi1=lambda :map(int1,input().split())
li1=lambda :list(mi1())
mis=lambda :map(str,input().split())
lis=lambda :list(mis())
pr=print

from collections import defaultdict
"""
#初期値 0
d=defaultdict(int)

#初期値 1
d=defaultdict(lambda:1)
"""

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())

mod=10**9+7
Mod=998244353
INF=10**18
ans=0

n=inp()
h=[0]*200001
w=[0]*200001
uf=UnionFind(200001)
for i in range(n):
  a,b=mi()
  h[a]+=1
  w[b]+=1
  uf.union(a,b)
x=0
y=0
for i in range(200001):
  if h[i]!=w[i]:
    if abs(h[i]-w[i])>1:
      print(0)
      exit()
    x+=1
  if h[i]>0:
    y+=1
t=0
for i in list(uf.all_group_members().values()):
  if len(i)!=1:
    t+=1
  else:
    if h[i[0]]!=0:
      t+=1
if t>1:
  print(0)
  exit()
if x==2:
  print(1)
elif x==0:
  print(y)
else:
  print(0)