#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
#define vec vector<ll>
#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=INF;
const ll inf=INF*INF;
//const ll mod=MOD;
const ll MAX=200010;

void dfs(ll u,vector<ll> &trail,vector<vector<ll> >&G){
    while(!G[u].empty()){
        ll v=G[u].back();
        G[u].pop_back();
        dfs(v,trail,G);
    }
    trail.push_back(u);
}

signed main(){
    ll n;cin>>n;
    vector<vector<ll> >G(MAX);
    vector<ll>in(MAX);
    vector<ll>out(MAX);
    ll s=-1,t=-1;
    rep(i,n){
        ll h,w;cin>>h>>w;
        h--;w--;
        out[w]++;
        in[h]++;
        G[h].pb(w);
    }
    ll cnt=0;
    ll kind=0;
    rep(i,MAX){
        if(in[i]==out[i]+1){
            s=i;
            cnt++;
        }else if(in[i]+1==out[i]){
            t=i;
            cnt++;
        }
        if(in[i]>0||out[i]>0)kind++;
    }
    if((cnt!=2&&cnt!=0)||(cnt==2&&(s==-1||t==-1))){
        cout<<0<<endl;
    }else{
        if(s==-1){
            rep(i,MAX){
                if(out[i]>0)s=i;
            }
        }
        vector<ll>trail(0);
        dfs(s,trail,G);
        if(trail.size()==n+1){
            if(cnt==2){
                cout<<1<<endl;
            }else{
                cout<<kind<<endl;
            }
        }else
        {
            cout<<0<<endl;
        }
        
    }
}