#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

#include <atcoder/dsu>

int main() {
    constexpr int lim = 200000;

    int n; cin >> n;

    auto g = vec<int>(uns, lim, 0);
    auto r = vec<int>(uns, lim, 0);
    auto h = vec<int>(uns, n);
    auto w = vec<int>(uns, n);
    for (int i = 0; i < n; ++i) {
        cin >> h[i] >> w[i]; --h[i]; --w[i];
        g[h[i]].push_back(w[i]);
        r[w[i]].push_back(h[i]);
    }

    atcoder::dsu dsu(lim);
    auto in = vec<int>(0, lim);
    auto out = vec<int>(0, lim);
    for (int i = 0; i < lim; ++i) {
        for (auto v : g[i]) {
            ++out[i]; --out[v];
            ++in[v]; --in[i];
            dsu.merge(i, v);
        }
    }

    for (int i = 0; i < n; ++i) {
        if (!dsu.same(h[0], h[i]) || !dsu.same(w[0], w[i])) {
            cout << 0 << endl;
            return 0;
        }
    }

    if (count(begin(out), end(out), 0) == lim) {
        set<int> ans;
        for (int i = 0; i < n; ++i) {
            ans.insert(h[i]);
            ans.insert(w[i]);
        }

        cout << size(ans) << endl;
        return 0;
    }

    if (1 < count(begin(in), end(in), 1) || 1 < count(begin(out), end(out), 1)) {
        cout << 0 << endl;
        return 0;
    }

    if (count(begin(in), end(in), 0) != lim - 2 || count(begin(out), end(out), 0) != lim - 2) {
        cout << 0 << endl;
        return 0;
    }

    cout << 1 << endl;
}