#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
const long long MOD = 1000000007;
const long long INF = 9999999999999999;
using ll = long long;
using mint = modint1000000007;
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; }
int main(){
  ll N;
  cin>>N;
  vector<vector<ll>> G(200200);
  vector<ll> aru;
  ll H[200200] = {};
  ll W[200200] = {};
  rep(i,N){
    ll a,b;
    cin>>a>>b;
    if(a == b){
      aru.push_back(a);
      continue;
    }
    H[a]++;
    W[b]++;
  }
  ll d = 0;
  rep(i,aru.size()){
    if(H[aru[i]] == 0 && W[aru[i]] == 0){
      d = 1;
    }
  }
  ll Hh = 0;
  ll Wh = 0;
  rep(i,200200){
    if(abs(H[i]-W[i]) > 1){
      d = 1;
    }
    else if(H[i]-W[i] == 1){
      Hh++;
    }
    else if(W[i]-H[i] == 1){
      Wh++;
    }
    else{
      continue;
    }
  }
  if(d){
    cout << 0 << endl;
    return 0;
  }
  if(Hh == 0 && Wh == 0){
    ll ans = 0;
    rep(i,200200){
      if(H[i]>0){
        ans++;
      }
    }
    cout << ans << endl;
  }
  else if(Hh == 1 && Wh == 1){
    cout << 1 << endl;
  }
  else{
    cout << 0 << endl;
  }
  return 0;
}