#include <bits/stdc++.h>

using i32 = std::int32_t;
using u32 = std::uint32_t;
using i64 = std::int64_t;
using u64 = std::uint64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

class rep {
    struct Iter {
        usize itr;
        constexpr Iter(const usize pos) noexcept : itr(pos) {}
        constexpr void operator++() noexcept { ++itr; }
        constexpr bool operator!=(const Iter& other) const noexcept { return itr != other.itr; }
        constexpr usize operator*() const noexcept { return itr; }
    };
    const Iter first, last;

  public:
    explicit constexpr rep(const usize first, const usize last) noexcept : first(first), last(std::max(first, last)) {}
    constexpr Iter begin() const noexcept { return first; }
    constexpr Iter end() const noexcept { return last; }
};

class UnionFind {
    usize components;
    std::vector<usize> data;

  public:
    explicit UnionFind(const usize size = 0) : components(size), data(size, (usize)-1) {}

    usize size() const { return data.size(); }
    usize count() const { return components; }

    usize leader(const usize u) {
        assert(u < size());
        if (data[u] >= size()) return u;
        return data[u] = leader(data[u]);
    }

    usize size(const usize u) {
        assert(u < size());
        return -data[leader(u)];
    }

    std::pair<usize, bool> merge(usize u, usize v) {
        assert(u < size());
        assert(v < size());
        u = leader(u);
        v = leader(v);
        if (u == v) return std::make_pair(u, false);
        if (data[u] > data[v]) std::swap(u, v);
        components -= 1;
        data[u] += data[v];
        data[v] = u;
        return std::make_pair(u, true);
    }

    bool same(const usize u, const usize v) {
        assert(u < size());
        assert(v < size());
        return leader(u) == leader(v);
    }

    std::vector<std::vector<usize>> decompose() {
        std::vector<std::vector<usize>> ret(size());
        for (const usize u : rep(0, size())) {
            ret[leader(u)].push_back(u);
        }
        ret.erase(std::remove_if(ret.begin(), ret.end(), [&](const std::vector<usize>& v) { return v.empty(); }),
                  ret.end());
        return ret;
    }
};

template <class T> using Vec = std::vector<T>;

void main_() {
    usize N;
    std::cin >> N;
    constexpr usize V = 200001;
    Vec<usize> in(V), out(V);
    UnionFind dsu(V);
    for (const auto i : rep(0, N)) {
        usize h, w;
        std::cin >> h >> w;
        in[w] += 1;
        out[h] += 1;
        dsu.merge(h, w);
    }
    usize start = 0, alive = 0;
    std::set<usize> comps;
    for (const auto i : rep(0, V)) {
        if (in[i] < out[i]) {
            if (in[i] + 1 == out[i]) {
                start += 1;
            } else {
                std::cout << "0\n";
                return;
            }
        }
        if (in[i] + out[i] > 0) {
            alive += 1;
            comps.insert(dsu.leader(i));
        }
    }
    if (start > 1 or comps.size() > 1) {
        std::cout << "0\n";
        return;
    }
    std::cout << (start == 1 ? 1 : alive) << '\n';
}

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    main_();
    return 0;
}