// Nachia くんだよ

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

const int Z = 200000;

int N;
vector<int> H,W;
vector<vector<int>> E;

int main() {
  cin >> N;
  H.assign(Z,0);
  W.assign(Z,0);
  E.resize(Z);
  rep(i,N){
    int h,w; cin >> h >> w; h--; w--;
    H[h]++;
    W[w]++;
    E[h].push_back(w);
  }
  
  int sH = -1;
  int dH = 0;
  rep(i,Z) if(H[i] > W[i]){
    dH += H[i] - W[i];
    sH = i;
  }
  if(dH > 1){ cout << 0 << "\n"; return 0; }

  vector<int> I = {sH};
  if(I.back() == -1) rep(i,Z) if(H[i] != 0) I.back() = i;
  int c = 0;
  rep(i,I.size()){
    int p = I[i];
    for(int e : E[p]) I.push_back(e);
    E[p].clear();
  }

  c = I.size() - 1;

  if(c != N) cout << "0\n";
  else if(sH == -1){
    int ans = 0;
    rep(i,Z) if(H[i] != 0) ans++;
    cout << ans << "\n";
  }
  else cout << "1\n";
  return 0;
}


struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_instance;