#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define each(e, v) for(auto &e: v)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
const int MOD = 1000000007;
//const int MOD = 998244353;
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
template<typename T> bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;};
template<typename T> bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;};

struct io_setup{
    io_setup(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

struct Union_Find_Tree{
    vector<int> data;
    const int n;
    
    Union_Find_Tree(int n) : data(n, -1), n(n) {}
    
    int root(int x){
        if(data[x] < 0) return x;
        return data[x] = root(data[x]);
    }

    int operator [] (int i) {return root(i);}
    
    bool unite(int x, int y){
        x = root(x), y = root(y);
        if(x == y) return false;
        if(data[x] > data[y]) swap(x, y);
        data[x] += data[y], data[y] = x;
        return true;
    }
    
    int size(int x) {return -data[root(x)];}
    
    bool same(int x, int y) {return root(x) == root(y);}
    
    void clear() {fill(begin(data), end(data), -1);}
};

int main(){
    int N; cin >> N;

    int MAX = 200000;
    vector<int> c(MAX+1, 0), d(MAX+1, 0);

    Union_Find_Tree uf(MAX+1);

    set<int> s;

    rep(i, N){
        int H, W; cin >> H >> W;
        c[H]++, d[W]++;
        s.insert(H), s.insert(W);
        uf.unite(H, W);
    }

    int id1 = -1, id2 = -1;
    int cnt1 = 0, cnt2 = 0;
    int K = 0;

    rep(i, MAX+1){
        if(c[i] > d[i]){
            cnt1 += c[i]-d[i];
            id1 = i;
        }
        if(c[i] < d[i]){
            cnt2 += d[i]-c[i];
            id2 = i;
        }
        if(c[i] > 0) K++;
    }

    //cout << cnt1 << '\n';

    if(cnt1 > 1 || uf.size(*s.begin()) != sz(s)) {cout << "0\n"; return 0;}

    if(id1 == -1) cout << K << '\n';
    else cout << "1\n";
}