#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>

#define mkp make_pair
#define mkt make_tuple
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(v) v.begin(), v.end()
using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
template <class T>
void chmin(T &a, const T &b) {
    if (a > b) a = b;
}
template <class T>
void chmax(T &a, const T &b) {
    if (a < b) a = b;
}

class DisjointSet {
public:
    int N;
    vector<int> rank, p;
    vector<int> sz;

    DisjointSet() {}
    DisjointSet(int n) : N(n), rank(n), p(n), sz(n) {
        for (int i = 0; i < N; i++) makeSet(i);
    }

    void makeSet(int x) {
        p[x] = x;
        rank[x] = 0;
        sz[x] = 1;
    }

    bool same(int x, int y) {
        return leader(x) == leader(y);
    }

    void unite(int x, int y) {
        if (same(x, y)) return;
        link(leader(x), leader(y));
    }

    void link(int x, int y) {
        if (rank[x] > rank[y]) swap(x, y);

        p[x] = y;
        sz[y] += sz[x];
        if (rank[x] == rank[y]) {
            ++rank[y];
        }
    }

    int leader(int x) {
        if (x != p[x]) p[x] = leader(p[x]);
        return p[x];
    }

    int size(int x) {
        return sz[leader(x)];
    }
};

const int MAX = 2e5 + 10;

void solve() {
    int N;
    cin >> N;
    vector<int> H(N), W(N);
    rep(i, N) cin >> H[i] >> W[i];

    {
        DisjointSet us(MAX);
        rep(i, N) us.unite(H[i], W[i]);
        int leader = us.leader(H[0]);
        rep(i, N) if (leader != us.leader(H[i])) {
            cout << 0 << endl;
            return;
        }
    }

    vector<int> in(MAX, 0), out(MAX, 0);
    rep(i, N) {
        in[W[i]]++;
        out[H[i]]++;
    }
    int s = -1, t = -1;
    for (int k = 0; k < MAX; k++) {
        if (in[k] - out[k] == 0) continue;
        if (in[k] - out[k] == 1) {
            if (t != -1) {
                cout << 0 << endl;
                return;
            }
            t = k;
        } else if (in[k] - out[k] == -1) {
            if (s != -1) {
                cout << 0 << endl;
                return;
            }
            s = k;
        } else {
            cout << 0 << endl;
            return;
        }
    }

    if (s == -1 && t == -1) {
        int cnt = 0;
        rep(k, MAX) if (in[k] > 0) cnt++;
        cout << cnt << endl;
    } else if (s == -1 || t == -1) {
        cout << 0 << endl;
    } else {
        cout << 1 << endl;
    }
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    solve();

    return 0;
}