#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001


int main(){
	
	int N;
	cin>>N;
	
	vector<int> da(200005,0),db(200005,0);
	
	dsu D(200005);
	
	rep(i,N){
		int h,w;
		cin>>h>>w;
		da[h]++;
		db[w]++;
		D.merge(h,w);
	}
	
	set<int> S;
	rep(i,da.size()){
		if(da[i]>0||db[i]>0){
			S.insert(D.leader(i));
		}
	}
	
	if(S.size()>1){
		cout<<0<<endl;
		return 0;
	}
	
	S.clear();
	set<int> S2;
	int cnt = 0;
	rep(i,da.size()){
		if(da[i]==0&&db[i]==0)continue;
		if(da[i]==db[i]){
			cnt++;
		}
		else if(da[i]+1==db[i]){
			S.insert(i);
		}
		else if(da[i]==db[i]+1){
			S2.insert(i);
		}
		else{
			cout<<0<<endl;
			return 0;
		}
	}
	
	if(S.size()==0&&S2.size()==0){
		cout<<cnt<<endl;
		return 0;
	}
	if(S.size()==1&&S2.size()==1){
		cout<<1<<endl;
		return 0;
	}
	
	cout<<0<<endl;
	
	return 0;
}