#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;

template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

struct UnionFind{
    private:
    vector<int> par,siz;

    public:
    int con;
    UnionFind(int n):par(n),siz(n,1),con(n){
        iota(begin(par),end(par),0);
    }
    int root(int x){
        return (par[x]==x?x:(par[x]=root(par[x])));
    }
    bool sameroot(int x,int y){
        return root(x)==root(y);
    }
    bool unite(int x,int y){
        x=root(x);y=root(y);
        if(x==y) return false;
        if(siz[x]<siz[y])swap(x,y);
        siz[x]+=siz[y];
        par[y]=x;
        con--;
        return true;
    }
    int size(int x){
        return siz[root(x)];
    }
};

signed main(){
    int N;cin>>N;
    vector<int> A(200001,0);
    UnionFind uf(200001);
    vector<int> vis;
    set<int> last;
    rep(i,N){
        int a,b;cin>>a>>b;
        A[a]++;
        A[b]--;
        vis.push_back(a);
        vis.push_back(b);
        last.insert(b);
        uf.unite(a,b);
    }

    set<int> st;
    for(auto &x:vis) st.insert(uf.root(x));
    if(st.size()>1){
        cout<<0<<endl;
        return 0;
    }

    int in=0,out=0;
    rep(i,200001){
        if(A[i]>1 or A[i]<-1){
            cout<<0<<endl;
            return 0;
        }

        if(A[i]==1)  in++;
        if(A[i]==-1) out++;
    }

    

    if(in==0 and out==0) cout<<last.size()<<endl;
    else if(in==1 and out==1) cout<<1<<endl;
    else cout<<0<<endl;
    return 0;
}