import sys
N = int(input())
HW = [list(map(int,input().split())) for _ in range(N)]

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):
        return {r: self.members(r) for r in self.roots()}
 
    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())
 
dic = {}
i = 0
for hw in HW:
    h,w = hw
    if not(h in dic):
        dic[h] = i
        i += 1
    if not(w in dic):
        dic[w] = i
        i += 1
n = i
uf = UnionFind(n)
for hw in HW:
    h,w = hw
    uf.union(dic[h],dic[w])

if uf.group_count() != 1:
    print(0)
    sys.exit()

MAX = 2*10**5+1
H = [[] for _ in range(MAX)]
W = [[] for _ in range(MAX)] 
for hw in HW:
    h,w = hw
    H[h].append(w)
    W[w].append(h)

cnt = 0
for i in range(MAX):
    cnt += abs(len(H[i]) - len(W[i]))
    if cnt > 2:
        print(0)
        sys.exit()
if cnt == 0:
    print(n)
else:
    print(1)