#include <bits/stdc++.h>
#define rep(i, l, r) for (int i = (l); i < (r); i++)
using namespace std;

typedef long long ll;

const int MAX_N = 200010;
int par[MAX_N];
int rnk[MAX_N];
int siz[MAX_N];

void init(int n) {
    rep(i,0,n) {
        par[i] = i;
        rnk[i] = 0;
        siz[i] = 1;
    }
}

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

void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;
    int s = siz[x] + siz[y];
    if (rnk[x] < rnk[y]) {
        par[x] = y;
    } else {
        par[y] = x;
        if (rnk[x] == rnk[y]) rnk[x]++;
    }
    siz[find(x)] = s;
}

bool same(int x, int y) {
    return find(x) == find(y);
}

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

int main() {
    int N, D = 0;
    cin >> N;
    init(200000);
    vector<int> A(200000, 0), B(200000, 0), H(N), W(N);
    rep(i, 0, N) {
        cin >> H[i] >> W[i];
        A[H[i] - 1]++;
        B[W[i] - 1]++;
        unite(H[i] - 1, W[i] - 1);
    }
    rep(i, 0, 200000) {
        if ((A[i] > 0 || B[i] > 0) && !same(i, H[0] - 1)) {
            cout << 0 << endl;
            return 0;
        }
        D += abs(A[i] - B[i]);
    }
    if (D > 2) {
        cout << 0 << endl;
    } else if (D == 2) {
        cout << 1 << endl;
    } else {
        int ans = 0;
        rep(i, 0, 200000) {
            ans += (A[i] > 0);
        }
        cout << ans << endl;
    }
}