class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n + 1)
        self.size = [1] * (n + 1)
 
    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 unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
            self.size[y] += self.size[x]
        else:
            self.par[y] = x
            self.size[x] += self.size[y]
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
 
    def same_check(self, x, y):
        return self.find(x) == self.find(y)

MAX = 2 * 10 ** 5
n = int(input())
g = [[] for _ in range(MAX + 1)]
inv = [0] * (MAX + 1)
out = [0] * (MAX + 1)
s = set()
uf = UnionFind(MAX + 1)
for i in range(n):
    h, w = map(int, input().split())
    uf.unite(h, w)
    s.add(h)
    s.add(w)
    g[h].append(w)
    inv[w] += 1
    out[h] += 1
f1 = 0
f2 = 0
v = [0] * (MAX + 1)
cnt = 0
for i in range(MAX + 1):
    j = uf.find(i)
    if j in s and v[j] == 0:
        v[j] = 1
        cnt += 1
    if inv[i] + 1 == out[i]:
        f1 += 1
    elif out[i] + 1 == inv[i]:
        f2 += 1
    elif inv[i] == out[i]:
        continue
    else:
        print(0)
        exit(0)
if cnt >= 2:
    print(0)
    exit(0)
if f1 == f2 == 0:
    print(len(s))
elif f1 == f2 == 1:
    print(1)
else:
    print(0)