class UnionFind:
    def __init__(self, n):
        self.parent = list(range(n)) #親ノード
        self.size = [1]*n #グループの要素数
 
    def root(self, x): #root(x): xの根ノードを返す．
        while self.parent[x] != x:
            self.parent[x] = self.parent[self.parent[x]]
            x = self.parent[x]
        return x 
 
    def merge(self, x, y): #merge(x,y): xのいる組とyのいる組をまとめる
        x, y = self.root(x), self.root(y)
        if x == y: return False
        if self.size[x] < self.size[y]: x,y=y,x #xの要素数が大きいように
        self.size[x] += self.size[y] #xの要素数を更新
        self.parent[y] = x #yをxにつなぐ
        return True
 
    def issame(self, x, y): #same(x,y): xとyが同じ組ならTrue
        return self.root(x) == self.root(y)
        
    def getsize(self,x): #size(x): xのいるグループの要素数を返す
        return self.size[self.root(x)]

n = int(input())
N = 2*10**5+1
ind = [0]*N
out = [0]*N
UF = UnionFind(N)
for _ in range(n):
    h,w = map(int,input().split())
    ind[h] += 1
    out[w] += 1
    UF.merge(h,w)
    r = UF.root(h)
nonzero = [i for i in range(N) if ind[i] != out[i]]
if len(nonzero) == 0:
    ans = sum(ind[i]+out[i] > 0 for i in range(N))
elif len(nonzero) == 2:
    i,j = nonzero
    if abs(ind[i] - out[i]) == 1:
        ans = 1
    else:
        ans = 0
else:
    ans = 0
for i in range(N):
    if (ind[i] or out[i]) and UF.root(i) != r:
        ans = 0
print(ans)