import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


class UnionFind:
    def __init__(self,n):
        self.par = [i for i in range(n+1)]  # 親のノード番号
        self.rank = [0]*(n+1)
        # self.conn_comp = [1]*(n+1)

    def find(self,x):  # xの根のノード番号
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def same_check(self,x,y):  # x,yが同じグループか否か
        return self.find(x) == self.find(y)

    def unite(self,x,y):  # x,yの属するグループの併合
        x = self.find(x)
        y = self.find(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.conn_comp[x] += self.conn_comp[y]

    # def connected_component(self,x):  # xの属する連結成分の大きさ
        # return self.conn_comp[self.find(x)]


N = I()

M = 2*10**5
in_deg = [0]*(M+1)
out_deg = [0]*(M+1)
UF = UnionFind(M)
for _ in range(N):
    H,W = MI()
    out_deg[H] += 1
    in_deg[W] += 1
    UF.unite(H,W)

a,b,c = 0,0,0
X = set()
for i in range(1,M+1):
    if (not in_deg[i]) and (not out_deg[i]):
        continue
    X.add(UF.find(i))
    if in_deg[i] == out_deg[i]:
        if in_deg[i]:
            a += 1
    elif in_deg[i] == out_deg[i]+1:
        b += 1
    elif in_deg[i]+1 == out_deg[i]:
        c += 1
    else:
        print(0)
        exit()

if b > 1 or c > 1 or b != c or len(X) > 1:
    print(0)
    exit()

if b:
    print(1)
else:
    print(a)