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

/*^ debug  */

template <typename A, typename B> string to_string(pair<A, B> p);
template <typename A, typename B, typename C> string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D> string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string) s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) { res += ", "; }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) { res += static_cast<char>('0' + v[i]); }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) { res += ", "; }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) { return "(" + to_string(p.first) + ", " + to_string(p.second) + ")"; }
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) { return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")"; }
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) { return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")"; }
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) { cerr << " " << to_string(H); debug_out(T...); }
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

/*  debug $*/

/*^ generic definitions  */

template<typename F>
struct _RecurFun : F {
  _RecurFun(F&& f) : F(forward<F>(f)) {}
  template<typename... Args>
  decltype(auto) operator()(Args&&... args) const { return F::operator()(*this, forward<Args>(args)...); }
};
template<typename F>
decltype(auto) RecurFun(F&& f) { return _RecurFun<F> { forward<F>(f) }; }

template<typename D, typename R>
vector<R> maps(const vector<D> &&d, function<R(D)> f) {
  vector<R> r(d.size());
  for (int i = 0; i < (int) d.size(); ++i) r[i] = f(d[i]);
  return r;
}

/*  generic definitions $*/

int main() {
  ios::sync_with_stdio(false);

  int N, M; { cin >> N >> M; }

  vector<int> B(N), C(N); {
    for (int i = 0; i < N; ++i) {
      cin >> B[i] >> C[i];
      --B[i], --C[i];
    }
  }

  vector<vector<int>> idxInB(M), idxInC(N); {
    for (int i = 0; i < N; ++i) {
      idxInB[B[i]].push_back(i);
      idxInC[C[i]].push_back(i);
    }
  }

  vector<int> fa(N);
  iota(fa.begin(), fa.end(), 0);
  function<int(int)> find = [&](int x) { return fa[x] == x ? x : fa[x] = find(fa[x]); };
  function<bool(int, int)> unite = [&](int x, int y) {
    if (find(x) == find(y)) return false;
    fa[find(x)] = find(y);
    return true;
  };

  int res = 0; {
    for (int b = 0; b < M; ++b) {
      for (int i = 0; i+1 < (int) idxInB[b].size(); ++i) {
        unite(idxInB[b][i], idxInB[b][i+1]);
      }
    }

    for (int c = 0; c < N; ++c) {
      for (int i = 0; i+1 < (int) idxInC[c].size(); ++i) {
        res += unite(idxInC[c][i], idxInC[c][i+1]);
      }
    }
  }

  cout << res << endl;
}