from collections import Counter


class UnionFind:
    __slots__ = ["n", "parent", "height", "size"]

    def __init__(self, n):
        self.n = n
        self.parent = [i for i in range(n)]
        self.height = [1] * n
        self.size = [1] * n

    def find(self, x):
        if self.parent[x] == x:
            return x
        else:
            self.parent[x] = self.find(self.parent[x])
            return self.parent[x]

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.height[x] < self.height[y]:
                self.parent[x] = y
                self.size[y] += self.size[x]
            else:
                self.parent[y] = x
                self.size[x] += self.size[y]
                if self.height[x] == self.height[y]:
                    self.height[x] += 1

    def issame(self, x, y):
        return self.find(x) == self.find(y)

    def group_size(self, x):
        return self.size[self.find(x)]

    def group_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.parent) if i == x]

    def group_count(self):
        return len(self.roots())


N = int(input())
MAX = 2 * 10**5
deg = [0] * MAX
st = set()
uf = UnionFind(MAX)
for _ in range(N):
    H, W = (int(x) - 1 for x in input().split())
    deg[H] += 1
    deg[W] -= 1
    uf.unite(H, W)
    st.add(H)
    st.add(W)

# 連結か
if len(set(uf.find(x) for x in st)) == 1:
    ct = Counter(deg)
    if ct[0] == MAX:
        print(len(st))
    elif ct[0] == MAX - 2 and ct[-1] == ct[1] == 1:
        print(1)
    else:
        print(0)
else:
    print(0)