#ifdef LOCAL
    #define _GLIBCXX_DEBUG
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
#endif
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

// #define INT128 // 必要なら有効化してください
#ifdef INT128
  using LL = __int128;
#endif

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(char c){
  string s = {c};
  return s;
}

// LL
#ifdef INT128
// input
istream& operator>>(istream& is, LL& v)
{
    string s;
    is >> s;
    v = 0;
    for (int i = 0; i < (int)s.size(); i++) {
        if (isdigit(s[i])) { v = v * 10 + s[i] - '0'; }
    }
    if (s[0] == '-') { v *= -1; }
    return is;
}
std::ostream &operator<<(std::ostream &dest, LL value) {
  std::ostream::sentry s(dest);
  if (s) {
    LL tmp = value < 0 ? -value : value;
    char buffer[128];
    char *d = std::end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (value < 0) {
      --d;
      *d = '-';
    }
    int len = std::end(buffer) - d;
    if (dest.rdbuf()->sputn(d, len) != len) {
      dest.setstate(std::ios_base::badbit);
    }
  }
  return dest;
}
string to_string(LL v){
  stringstream ss;
  ss << v;
  return ss.str();
}
#endif // LL

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set 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 (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())
#define MP make_pair
#define p_yes() p("Yes")
#define p_no() p("No")
#define p_possible() p("Possible")
#define p_impossible() p("Impossible")
void yes(){p_yes(); exit(0);}
void no(){p_no(); exit(0);}
void possible(){p_possible(); exit(0);}
void impossible(){p_impossible(); exit(0);}

ll SUM(VI& V){
  return accumulate(ALL(V), 0LL);
}

ll MIN(VI& V){return *min_element(ALL(V));}
ll MAX(VI& V){return *max_element(ALL(V));}

void print_vector(VI& V, ll offset=0){
  ll n = V.size();
  rep(i, n){
    if(i) cout << ' ';
    cout << V[i]+offset;
  }
  cout << endl;
}

ll gcd(ll a,ll b){
    if(b == 0) return a;
    return gcd(b,a%b);
}

ll lcm(ll a,ll b){
    ll g = gcd(a,b);
    return a / g * b;
}

// long double
using ld = long double;
// #define EPS (1e-14)
constexpr ld EPS = 1e-14;
// #define equals(a,b) (fabs((a)-(b)) < EPS)
constexpr bool equals(ld a, ld b){return fabs((a)-(b)) < EPS;}

// 小さい順に取り出すpriority queue
using inverse_priority_queue = priority_queue<ll, vector<ll>, greater<ll> >;

int popcount(ll t){
    return __builtin_popcountll(t);
}

const ll mod = 1e9 + 7;
// const ll mod = 998244353;
const ll inf = 1e18;
const double PI = acos(-1);

// [a/b] (繰り上げ)
ll ceil_div(ll a, ll b){
  return (a+b-1)/b;
}

ll ll_pow(ll a, ll n){
    ll ans = 1;
    FOR(i, 0, n){
        ans *= a;
    }
    return ans;
}
// modなし

// snuke's mint
// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
// const int mod = 1000000007;
struct mint {
  ll x; // using ll = long long;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res+=a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res-=a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res*=a;
  }
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const {
    return pow(mod-2);
  }
  mint& operator/=(const mint a) {
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const {
    mint res(*this);
    return res/=a;
  }
};

// N : 頂点数
// M : 辺数
// return vector<vector<ll>>
VV load_graph(ll N, ll M){
  VV G(N);
  rep(i,M){
    ll a,b;cin>>a>>b;
    a--;b--;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  return G;
}
VV load_tree(ll N){
  return load_graph(N, N-1);
}

//#include <atcoder/dsu>
//using namespace atcoder; // 忘れがち

// 座標圧縮
// 変換テーブルを返す
VI make_compress_table(vector<ll>& A){  
  // 変換表
  auto B = A;
  sort(ALL(B));
  auto it = unique(ALL(B));
  B.erase(it, B.end());
  return B;
}
ll compress_by_table(VI& T, ll v){
  return lower_bound(ALL(T), v) - T.begin();
}

// オイラー路ライブラリ
// そもそも連結されているか (by BFS)
bool is_connected(VV& G){
  ll N = G.size();
  vector<bool> visited(N);
  ll sid = 0; // start id
  visited[sid] = true;
  queue<ll> que;
  que.push(sid);
  while(!que.empty()){
    ll id = que.front(); que.pop();
    for(ll to : G[id]){
      if(!visited[to]){
        que.push(to);
        visited[to] = true;
      }
    }
  }
  rep(i, N){
    if(!visited[i]) return false;
  }
  return true;
}
// ※有向
// オイラー閉路が作れるか？
// 条件：すべての頂点について入次数＝出次数
bool is_eular_circuit(VV& G){
  ll N = G.size();
  VI in(N);
  VI out(N);
  rep(i,N){
    for(ll j : G[i]){
      // i to j
      out[i]++;
      in[j]++;
    }
  }
  rep(i,N){
    if(in[i]!=out[i])return false;
  }
  return true;
}
// ※有向
// オイラー路が作れるか？
// 条件：
// ある１点について、入次数＋１＝出次数
// ある１点について、入次数＝出次数＋１
// その他の点について、入次数＝出次数
bool is_eular_trail(VV& G){
  ll N = G.size();
  VI in(N);
  VI out(N);
  rep(i,N){
    for(ll j : G[i]){
      // i to j
      out[i]++;
      in[j]++;
    }
  }
  ll more_in=0;
  ll more_out=0;
  ll even=0;
  rep(i,N){
    if(in[i]==out[i]){
      even++;
    }
    else if(in[i]>out[i]){
      more_in++;
    }
    else{
      more_out++;
    }
  }
  if(more_in==1 && more_out==1)return true;
  return false;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N;
    cin>>N;
    
    VI H(N);
    VI W(N);
    rep(i,N)cin>>H[i]>>W[i];

    VI A;
    rep(i,N){
      A.push_back(H[i]);
      A.push_back(W[i]);
    }
    auto tbl = make_compress_table(A);
    
    // graph size M
    ll M = tbl.size();
    VV G(M);
    // edge
    rep(i,N){
      ll h=H[i];
      ll w=W[i];
      // h to w
      ll a = compress_by_table(tbl, h);
      ll b = compress_by_table(tbl, w);
      // a to b
      G[a].push_back(b);
    }

    if(!is_connected(G)){
      p(0);return 0;
    }

    if(is_eular_circuit(G)){
      p(M);return 0;
    }

    if(is_eular_trail(G)){
      p(1);return 0;
    }

    p(0);
    return 0;
}