#include #define FOR(i, n, m) for(ll i = (n); i < (ll)(m); i++) #define REP(i, n) FOR(i, 0, n) #define ALL(v) v.begin(), v.end() #define pb push_back using namespace std; using ll = long long; using ld = long double; using P = pair; constexpr ll inf = 1000000000; constexpr ll mod = 1000000007; constexpr long double eps = 1e-6; template ostream& operator<<(ostream& os, pair p) { os << to_string(p.first) << " " << to_string(p.second); return os; } template ostream& operator<<(ostream& os, vector& v) { REP(i, v.size()) { if(i) os << " "; os << v[i]; } return os; } struct modint { ll n; public: modint(const ll n = 0) : n((n % mod + mod) % mod) {} static modint pow(modint a, int m) { modint r = 1; while(m > 0) { if(m & 1) { r *= a; } a = (a * a); m /= 2; } return r; } modint &operator++() { *this += 1; return *this; } modint &operator--() { *this -= 1; return *this; } modint operator++(int) { modint ret = *this; *this += 1; return ret; } modint operator--(int) { modint ret = *this; *this -= 1; return ret; } modint operator~() const { return (this -> pow(n, mod - 2)); } // inverse friend bool operator==(const modint& lhs, const modint& rhs) { return lhs.n == rhs.n; } friend bool operator<(const modint& lhs, const modint& rhs) { return lhs.n < rhs.n; } friend bool operator>(const modint& lhs, const modint& rhs) { return lhs.n > rhs.n; } friend modint &operator+=(modint& lhs, const modint& rhs) { lhs.n += rhs.n; if (lhs.n >= mod) lhs.n -= mod; return lhs; } friend modint &operator-=(modint& lhs, const modint& rhs) { lhs.n -= rhs.n; if (lhs.n < 0) lhs.n += mod; return lhs; } friend modint &operator*=(modint& lhs, const modint& rhs) { lhs.n = (lhs.n * rhs.n) % mod; return lhs; } friend modint &operator/=(modint& lhs, const modint& rhs) { lhs.n = (lhs.n * (~rhs).n) % mod; return lhs; } friend modint operator+(const modint& lhs, const modint& rhs) { return modint(lhs.n + rhs.n); } friend modint operator-(const modint& lhs, const modint& rhs) { return modint(lhs.n - rhs.n); } friend modint operator*(const modint& lhs, const modint& rhs) { return modint(lhs.n * rhs.n); } friend modint operator/(const modint& lhs, const modint& rhs) { return modint(lhs.n * (~rhs).n); } }; istream& operator>>(istream& is, modint m) { is >> m.n; return is; } ostream& operator<<(ostream& os, modint m) { os << m.n; return os; } #define MAX_N 1010101 long long extgcd(long long a, long long b, long long& x, long long& y) { long long d = a; if (b != 0) { d = extgcd(b, a % b, y, x); y -= (a / b) * x; } else { x = 1; y = 0; } return d; } long long mod_inverse(long long a, long long m) { long long x, y; if(extgcd(a, m, x, y) == 1) return (m + x % m) % m; else return -1; } vector fact(MAX_N+1, inf); long long mod_fact(long long n, long long& e) { if(fact[0] == inf) { fact[0]=1; if(MAX_N != 0) fact[1]=1; for(ll i = 2; i <= MAX_N; ++i) { fact[i] = (fact[i-1] * i) % mod; } } e = 0; if(n == 0) return 1; long long res = mod_fact(n / mod, e); e += n / mod; if((n / mod) % 2 != 0) return (res * (mod - fact[n % mod])) % mod; return (res * fact[n % mod]) % mod; } // return nCk long long mod_comb(long long n, long long k) { if(n < 0 || k < 0 || n < k) return 0; long long e1, e2, e3; long long a1 = mod_fact(n, e1), a2 = mod_fact(k, e2), a3 = mod_fact(n - k, e3); if(e1 > e2 + e3) return 0; return (a1 * mod_inverse((a2 * a3) % mod, mod)) % mod; } using mi = modint; mi mod_pow(mi a, ll n) { mi ret = 1; mi tmp = a; while(n > 0) { if(n % 2) ret *= tmp; tmp = tmp * tmp; n /= 2; } return ret; } ll mod_pow(ll a, ll n, ll m) { ll ret = 1; ll tmp = a; while(n > 0) { if(n % 2) ret *= tmp; ret %= m; tmp = tmp * tmp; tmp %= m; n /= 2; } return ret % m; } ll gcd(ll a, ll b) { if (b == 0) return a; return gcd(b, a % b); } struct UnionFind { vector< int > data; UnionFind(int sz) { data.assign(sz, -1); } bool unite(int x, int y) { x = find(x), y = find(y); if(x == y) return (false); if(data[x] > data[y]) swap(x, y); data[x] += data[y]; data[y] = x; return (true); } int find(int k) { if(data[k] < 0) return (k); return (data[k] = find(data[k])); } int size(int k) { return (-data[find(k)]); } }; int main() { cin.tie(0); ios::sync_with_stdio(false); int n, m; cin >> n >> m; vector> slime(n); REP(i, n) { int b, c; cin >> b >> c; slime[c - 1].pb(b - 1); } UnionFind uf(m); REP(i, n) { if(slime[i].empty()) continue; for(auto elm: slime[i]) { uf.unite(slime[i][0], elm); } } set seen; int ans = n - 1; REP(i, m) { if(not seen.count(uf.find(i))) { ans -= 1; seen.insert(uf.find(i)); } } cout << ans << endl; return 0; }