#include<algorithm>
#include<iostream>
#include<vector>
#include<map>
#include<cassert>
#include<set>
using namespace std;
using ll = long long;

#include<atcoder/dsu>

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

    int n;
    cin>>n;
    atcoder::dsu uf(2<<17);
    vector<int> use(2<<17,0),cnt(2<<17,0);
    for(int i = 0;i<n;i++){
        int h,w;
        cin>>h>>w;
        cnt[h]++;
        cnt[w]--;
        use[h] = 1;
        use[w] = 1;
        uf.merge(h,w);
    }
    set<int> s;
    int a = 0;
    int b = 0;
    bool fn = true;
    int ans = 0;
    for(int i = 0;i<2<<17;i++){
        if(use[i]==0) continue;
        if(cnt[i]==1) a++;
        if(cnt[i]==-1) b++;
        ans++;
        s.insert(uf.leader(i));
        if(abs(cnt[i])>=2) fn = false;
    }
    if(s.size()>=2) fn = false;
    if(!fn){
        cout<<0<<endl;
        return 0;
    }

    if(a==0&&b==0){
        cout<<ans<<endl;
        return 0;
    }
    if(a==1&&b==1){
        cout<<1<<endl;
        return 0;
    }
    cout<<0<<endl;

}