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

#define REP(i,n) for(ll i=0;i<(ll)n;i++)
#define dump(x)  cerr << "Line " << __LINE__ << ": " <<  #x << " = " << (x) << "\n";
#define spa << " " <<
#define fi first
#define se second
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()

using ld = long double;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<ld, ld>;

template<typename T> using V = vector<T>;
template<typename T> using P = pair<T, T>;
template<typename T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<typename... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }
template<class S, class T> ostream& operator << (ostream& os, const pair<S, T> v){os << "(" << v.first << ", " << v.second << ")"; return os;}
template<typename T> ostream& operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<vector<T>> &v){ for(auto &e : v){os << e << "\n";} return os;}
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;

template <class T> void UNIQUE(vector<T> &x) {sort(ALL(x));x.erase(unique(ALL(x)), x.end());}
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
void fail() { cout << -1 << '\n'; exit(0); }
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
template<typename T> void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cerr<<v[i][0];for(ll j=1;j<w;j++)cerr spa v[i][j];cerr<<"\n";}};
template<typename T> void debug(vector<T>&v,ll n){if(n!=0)cerr<<v[0];
for(ll i=1;i<n;i++)cerr spa v[i];
cerr<<"\n";};

const ll INF = (1ll<<62);
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const ll mod = (int)1e9 + 7;
//const ll mod = 998244353;

// par[i]  は，iがrootなら-(連結成分のサイズ)を，iがrootではないならばrootを返す
// root(x) は必ずroot を返す
struct UnionFindSize {
    vector<int> par;
    
    UnionFindSize(int n) : par(n, -1) { }
    void init(int n) { par.assign(n, -1); }
    
    int root(int x) {
        if (par[x] < 0) return x;
        else return par[x] = root(par[x]);
    }
    
    bool issame(int x, int y) {
        return root(x) == root(y);
    }
    
    bool merge(int x, int y) {
        x = root(x); y = root(y);
        if (x == y) return false;
        if (par[x] > par[y]) swap(x, y); // merge technique
        par[x] += par[y];
        par[y] = x;
        return true;
    }
    
    int size(int x) {
        return -par[root(x)];
    }

    void print(){
        cout << "uf: ";
        for(int i=0;i<(int)par.size();i++) cout << root(i) << " ";
        cout << endl;
    }
};

template<typename T>
tuple<map<T, int>, vector<T>> compress(const vector<T> &X){
    vector<T> decoder = X;
    sort(decoder.begin(), decoder.end());
    decoder.erase(unique(decoder.begin(), decoder.end()), decoder.end());
    map<T, int> encoder;
    for(int i=0;i<(int)decoder.size();i++) encoder[decoder[i]] = i;
    return {encoder, decoder};
}

int main(){

    ll N;
    cin >> N;
    V<ll> H(N), W(N);
    REP(i, N) cin >> H[i] >> W[i];

    V<ll> tmp;
    REP(i, N) tmp.push_back(H[i]), tmp.push_back(W[i]);
    auto [enc, dec] = compress(tmp);
    ll csz = dec.size();
    UnionFindSize uf(csz);
    REP(i, N) uf.merge(enc[H[i]], enc[W[i]]);

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

    ll sz = 202020;
    V<V<ll>> G(sz);
    V<ll> in_deg(sz, 0), out_deg(sz, 0);
    REP(i, N){
        out_deg[H[i]]++;
        in_deg[W[i]]++;
    }

    bool cycle = true;
    REP(i, sz){
        if(out_deg[i] - in_deg[i] != 0) cycle = false;
    }

    set<ll> st;
    REP(i, N) st.insert(H[i]), st.insert(W[i]);
    ll M = st.size();

    ll res = 0;
    if(cycle){
        res = M;
    }else{
        V<ll> cnt(3, 0);
        REP(i, sz){
            ll v = out_deg[i] - in_deg[i];
            if(v == -1) cnt[0]++;
            else if(v == 0) cnt[1]++;
            else if(v == 1) cnt[2]++;
        }
        if(cnt[0] == 1 and cnt[1] == sz-2 and cnt[2] == 1){
            res = 1;
        }else{
            res = 0;
        }
    }

    cout << res << endl;
    return 0;
}