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

struct UnionFind {
    UnionFind(int n) : p(n, -1) {}
    int root(int u) {
        return p[u] < 0 ? u : p[u] = root(p[u]);
    }
    int size(int u) {
        return -p[root(u)];
    }
    bool same(int u, int v) {
        return root(u) == root(v);
    }
    bool unite(int u, int v) {
        u = root(u);
        v = root(v);
        if (u == v) return false;
        if (p[u] > p[v]) swap(u, v);
        p[u] += p[v];
        p[v] = u;
        return true;
    }
    vector<int> p;
};

int main() {
    int n;
    cin >> n;

    UnionFind uf((int)2e5 + 1);
    unordered_map<int, int> mp;
    for (int i = 0; i < n; i++) {
        int h, w;
        cin >> h >> w;

        uf.unite(h, w);
        mp[h]--;
        mp[w]++;
    }

    if (uf.size(mp.begin()->first) != mp.size()) {
        cout << 0 << endl;
        exit(0);
    }

    int x = 0;
    for (const auto &[i, d] : mp) {
        x += abs(d);
    }
    if (x == 0) {
        cout << mp.size() << endl;
    } else if (x == 2) {
        cout << 1 << endl;
    } else {
        cout << 0 << endl;
    }

    return 0;
}