#include <bits/stdc++.h>
using namespace std;

template <class A, class B> bool cmin(A& a, B b) { return a > b && (a = b, true); }
template <class A, class B> bool cmax(A& a, B b) { return a < b && (a = b, true); }

class UnionFind {
private:
  long N;
  vector<long> PS;

public:
  UnionFind() : N(0) {}
  UnionFind(long n) : N(n), PS(n, -1) {}
  bool unite(long a, long b) {
    long x = root(a), y = root(b);
    if (x == y) return false;
    if (-PS.at(x) < -PS.at(y)) swap(x, y);
    PS.at(x) += PS.at(y);
    PS.at(y) = x;
    return true;
  }
  bool same(long a, long b) { return root(a) == root(b); }
  long root(long a) {
    if (PS.at(a) < 0) return a;
    return PS.at(a) = root(PS.at(a));
  }
  long size(long a) { return -PS.at(root(a)); }
  vector<vector<long>> groups() {
    vector<long> B(N), S(N);
    for (long i = 0; i < N; i++) {
      B.at(i) = root(i);
      S.at(B.at(i))++;
    }
    vector<vector<long>> ret(N);
    for (long i = 0; i < N; i++) {
      ret.at(i).reserve(S.at(i));
    }
    for (long i = 0; i < N; i++) {
      ret.at(B.at(i)).push_back(i);
    }
    auto f = [&](const vector<long> &v) { return v.empty(); };
    ret.erase(remove_if(ret.begin(), ret.end(), f), ret.end());
    return ret;
  }
};

signed main() {
  cin.tie(nullptr)->sync_with_stdio(false);

  long N, M;
  cin >> N >> M;
  vector<pair<long, long>> V(N);
  for (long i = 0; i < N; i++) {
    long a, b;
    cin >> a >> b, a--, b--;
    V.at(i) = {a, b};
  }

  UnionFind UF(M);
  vector<vector<long>> G(N);
  for (const auto& [a, b] : V) G.at(b).push_back(a);
  long ans = 0;
  for (const auto& g : G) {
    if ((long)g.size() <= 1) continue;
    long tmp = UF.root(g.front());
    for (const auto& a : g) {
      if (UF.root(a) != tmp) {
        UF.unite(g.front(), a);
        ans++;
      }
    }
  }
  cout << ans << '\n';
}