#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>

using namespace std;
using ll = long long;

struct UnionFind {
    int ngroup;
    vector<int> par;
    vector<int> siz;

    UnionFind(int N) : par(N), siz(N) {
        ngroup = N;
        for(int i = 0; i < N; i++){
            par[i] = i;
            siz[i] = 1;
        }
    }

    int root(int x) {
        if (par[x] == x) return x;
        return par[x] = root(par[x]);
    }

    int unite(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        if (rx == ry) return rx;
        ngroup--;
        if (siz[rx] > siz[ry]) swap(rx, ry);
        par[rx] = ry;
        siz[ry] += siz[rx];
        return ry;
    }

    bool same(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }

    int size(int x){
        return siz[root(x)];
    }

    int group_count(){
        return ngroup;
    }
};

int main(){
 
    int N, p=0, m=0, z=0, a, b, M=2e5, K=0;
    cin >> N;
    UnionFind tree(M+1);
    vector<ll> cnt(M+1);
    vector<bool> visit(M+1);
 
    for (int i=0; i<N; i++){
        cin >> a >> b;
        tree.unite(a, b);
        cnt[a]--;
        cnt[b]++;
        if (!visit[a]){
            K++;
            visit[a] = 1;
        }
        if (!visit[b]){
            K++;
            visit[b] = 1;
        }
    }

    for (int i=1; i<=M; i++){
        if (!visit[i]) continue;
        if (cnt[i] == 0) z++;
        else if (cnt[i] == 1) p++;
        else if (cnt[i] == -1) m++;
    }

    if (tree.size(a) != K) cout << 0 << endl;
    else{
        if (z == K) cout << K << endl;
        else if (p == 1 && m == 1 && z == (K-2)) cout << 1 << endl;
        else cout << 0 << endl;
    }
 
    return 0;
}