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

    def all_group_members(self):
        dic = {r:[] for r in self.roots()}
        for i in range(self.n):
            dic[self.find(i)].append(i)
        return dic

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n = int(input())
max_ = 2 * 10 ** 5
UF = UnionFind(max_)
edges = [[] for _ in range(max_)]
in_cnt = [0] * max_
out_cnt = [0] * max_
for _ in range(n):
    h, w = map(int, input().split())
    h -= 1
    w -= 1
    UF.union(h, w)
    edges[h].append(w)
    in_cnt[h] += 1
    out_cnt[w] += 1
    
for i, o in enumerate(out_cnt):
    if o != 0:
        break
s = i
for j, o in enumerate(out_cnt):
    if o != 0:
        if not UF.same(s, j):
            print(0)
            exit()

    
s = -1
g = -1

for j, (i, o) in enumerate(zip(in_cnt, out_cnt)):
    if i == o:
        continue
    if i == o + 1:
        if s == -1:
            s = j
        else:
            print(0)
            exit()
    elif i + 1 == o:
        if g == -1:
            g = j
        else:
            print(0)
            exit()
    else:
        print(0)
        exit()

if s == g == -1:
    ans = 0
    for e in edges:
        if e: ans += 1
    print(ans)
else:
    print(1)