import sys
readline = sys.stdin.readline
from collections import Counter

from bisect import *
from copy import deepcopy
def compress(lst):
    """
    B: lstを座圧したリスト
    D: 元の値からindexを取得する辞書
    """
    B = []
    D = dict()
    vals = deepcopy(lst)
    vals = list(set(vals))
    vals.sort()
    for i in range(len(lst)):
        ind = bisect_left(vals, lst[i])
        B.append(ind)
    for i in range(len(B)):
        D[lst[i]] = B[i]
    return B, D

class UnionFind(object):
    def __init__(self, n=1):
        self.par = [i for i in range(n)]
        self.rank = [0 for _ in range(n)]
        self.size = [1 for _ in range(n)]

    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.rank[x] < self.rank[y]:
                x, y = y, x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
            self.par[y] = x
            self.size[x] += self.size[y]

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

    def get_size(self, x):
        x = self.find(x)
        return self.size[x]



N = int(readline())
H, W = [0] * N, [0] * N
for i in range(N):
    H[i], W[i] = map(int, readline().split())
D, _ = compress(H + W)
M = max(D) + 1
deg = [0] * M

U = UnionFind(M)
for i in range(N):
    U.union(D[i], D[i + N])
    deg[D[i]] += 1
    deg[D[i + N]] -= 1

if U.get_size(0) != M:
    print(0)
    exit()

c = Counter(deg)
if c[0] == M:
    print(M)
elif c[0] == M - 2 and c[1] == c[-1] == 1:
    print(1)
else:
    print(0)