#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int INF = 1000000000;
const ll INFL = 2e18;
template <class T>bool chmin(T &a, T b){ if (a > b) { a = b; return true;} else return false;}
template <class T>bool chmax(T &a, T b){ if (a < b) { a = b; return true;} else return false;}

class UnionFind {
public:
    vector<int> par;
    vector<int> siz;

    UnionFind() {
    }

    UnionFind(int sz_): par(sz_), siz(sz_, 1) {
        for(int i = 0;i < sz_;i++)par[i] = i;
    }

    void init(int sz_) {
        par.resize(sz_);
        siz.resize(sz_,1);
        for(int i = 0;i < sz_;i++)par[i] = i;
    }

    int root(int x) {
        while (par[x] != x) {
            x = par[x] = par[par[x]];
        }
        return x;
    }

    bool merge(int x,int y) {
        x = root(x);
        y = root(y);
        if(x == y)return false;
        if(siz[x] < siz[y])swap(x, y);
        siz[x] += siz[y];
        par[y] = x;
        return true;
    }

    bool issame(int x, int y) {
        return root(x) == root(y);
    }

    int size(int x) {
        return siz[root(x)];
    }
};
int main() {
    int N;
    cin >> N;

    vector<int> H(N);
    vector<int> W(N);
    map<int,int> mp;
    for (int i = 0;i < N;i++){
        cin >> H[i] >> W[i];
        mp[H[i]] = mp[W[i]] = 1;
    }

    int idx = 0;
    for (auto& p:mp) {
        p.second = idx;
        idx++;
    }

    UnionFind uf(mp.size());
    vector<int> in_deg(mp.size(), 0);
    vector<int> out_deg(mp.size(), 0);
    for (int i = 0;i < N;i++) {
        H[i] = mp[H[i]], W[i] = mp[W[i]];
        uf.merge(H[i], W[i]);
        in_deg[W[i]]++;
        out_deg[H[i]]++;
    }

    if (uf.size(0) != mp.size()) {
        cout << 0 << endl;
        return 0;
    }

    int cnt_0 = 0;
    int cnt_p1 = 0;
    int cnt_m1 = 0;
    for (int i = 0;i < mp.size();i++) {
        int deg = in_deg[i] - out_deg[i];
        if (deg == 0)cnt_0++;
        if (deg == -1)cnt_m1++;
        if (deg == 1)cnt_p1++;
    }

    if (cnt_0 == mp.size()) {
        cout << mp.size() << endl;
    }
    else if(cnt_m1 == 1 && cnt_p1 == 1 && cnt_0 + cnt_m1 + cnt_p1 == mp.size()) {
        cout << 1 << endl;
    }
    else cout << 0 << endl;
}