#include <bits/stdc++.h>
using namespace std;

struct UnionFind{
    vector<int> parent;
    vector<int> numberOfElements;//根ノードのみ有効
    UnionFind(int n){
        parent.resize(n);
        numberOfElements.resize(n);
        for(int i=0;i<n;++i){
            parent[i]=-1;
            numberOfElements[i]=1;
        }
    }
    int find(int a){
        vector<int> path(0);
        int pointer=a;
        while(parent[pointer]!=-1){
            path.push_back(pointer);
            pointer=parent[pointer];
        }
        for(int i:path){
            parent[i]=pointer;
        }
        return pointer;
    }
    void unite(int a,int b){
        int p=find(a);
        int q=find(b);
        if(p==q){
            return;
        }
        if(numberOfElements[p]<numberOfElements[q]){
            parent[p]=q;
            numberOfElements[q]+=numberOfElements[p];
        }else{
            parent[q]=p;
            numberOfElements[p]+=numberOfElements[q];
        }
    }
};

int main(){
    int N,temp=0,check=0;
    cin>>N;
    map<int,int> cnt;
    vector<vector<int>> a(N,vector<int>(2));
    for(int i=0;i<N;++i){
        for(int j=0;j<2;++j){
            cin>>a[i][j];
            cnt[a[i][j]]+=j*2-1;
        }
    }
    int p=cnt.size();
    map<int,int> comp;
    for(auto i=cnt.begin();i!=cnt.end();++i){
        comp[i->first]=temp;
        ++temp;
        check+=abs(i->second);
    }
    UnionFind U(p);
    for(vector<int> v:a){
        U.unite(comp[v[0]],comp[v[1]]);
    }
    temp=U.find(comp[a[0][0]]);
    for(auto i=cnt.begin();i!=cnt.end();++i){
        if(U.find(comp[i->first])!=temp){
            cout<<0<<endl;
            return 0;
        }
    }
    if(check>2){
        cout<<0<<endl;
    }else if(check){
        cout<<1<<endl;
    }else{
        cout<<p<<endl;
    }
}