#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define int long long #define ii pair #define app push_back #define all(a) a.begin(), a.end() #define bp __builtin_popcountll #define ll long long #define mp make_pair #define x first #define y second #define Time (double)clock()/CLOCKS_PER_SEC #define debug(x) std::cerr << #x << ": " << x << '\n'; #define FORI(i,a,b) for (int i = (a); i < (b); ++i) #define FOR(i,a) FORI(i,0,a) #define ROFI(i,a,b) for (int i = (b)-1; i >= (a); --i) #define ROF(i,a) ROFI(i,0,a) #define rep(a) FOR(_,a) #define each(a,x) for (auto& a: x) #define FORN(i, n) FORI(i, 1, n + 1) using vi = vector; template std::istream& operator >>(std::istream& input, std::pair & data) { input >> data.x >> data.y; return input; } template std::istream& operator >>(std::istream& input, std::vector& data) { for (T& x : data) input >> x; return input; } template std::ostream& operator <<(std::ostream& output, const pair & data) { output << "(" << data.x << "," << data.y << ")"; return output; } template std::ostream& operator <<(std::ostream& output, const std::vector& data) { for (const T& x : data) output << x << " "; return output; } std::ostream& operator <<(std::ostream& output, const __int128 &x) { __int128 n = x; if (n == 0) { output << "0"; return output; } if (n < 0) { n = -n; output << "-"; } string s; while (n) { s += '0' + (n%10); n /= 10; } reverse(all(s)); cout << s; return output; } ll div_up(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up ll div_down(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down ll math_mod(ll a, ll b) { return a - b * div_down(a, b); } #define tcT template using V = vector; tcT> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; } // set a = min(a,b) tcT> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; } ll gcd(ll a, ll b) { while (b) { tie(a, b) = mp(b, a % b); } return a; } int Bit(int mask, int bit) { return (mask >> bit) & 1; } const int N = 2e5+7; vi g[N]; bool used[N]; void dfs(int u) { used[u] = 1; each (v, g[u]) { if (!used[v]) { dfs(v); } } } int in[N], out[N]; signed main() { #ifdef LOCAL #else #define endl '\n' ios_base::sync_with_stdio(0); cin.tie(0); #endif int n; cin >> n; int some = -1; set comp; rep (n) { int u, v; cin >> u >> v; out[u]++; in[v]++; some = u; g[u].app(v); g[v].app(u); comp.insert(u); comp.insert(v); } dfs(some); FOR (i, N) { if (g[i].size() && !used[i]) { cout << 0 << endl; exit(0); } } vi cnt(2); FOR (i, N) { if (in[i] != out[i]) { if (in[i] == out[i] + 1) { cnt[0]++; } else if (out[i] == in[i] + 1) { cnt[1]++; } else { cout << 0 << endl; exit(0); } } } if (cnt[0] == 0 && cnt[1] == 0) { cout << comp.size() << endl; } else if (cnt[0] == 1 && cnt[1] == 1) { cout << 1 << endl; } else { cout << 0 << endl; } }