#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

struct UnionFind {
  UnionFind(int n) : data(n, -1) {}

  int root(int ver) { return data[ver] < 0 ? ver : data[ver] = root(data[ver]); }

  bool unite(int u, int v) {
    u = root(u);
    v = root(v);
    if (u == v) return false;
    if (data[u] > data[v]) std::swap(u, v);
    data[u] += data[v];
    data[v] = u;
    return true;
  }

  bool same(int u, int v) { return root(u) == root(v); }

  int size(int ver) { return -data[root(ver)]; }

private:
  std::vector<int> data;
};

int main() {
  int n, m; cin >> n >> m;
  vector<int> b(n), c(n); REP(i, n) cin >> b[i] >> c[i], --b[i], --c[i];
  vector<set<int>> box(m);
  REP(i, n) box[b[i]].emplace(c[i]);
  UnionFind uf(n);
  for (const set<int> &st : box) {
    if (st.empty()) continue;
    for (auto it = next(st.begin()); it != st.end(); ++it) uf.unite(*prev(it), *it);
  }
  map<int, set<int>> mp;
  vector<int> cnt(m, 0);
  REP(i, n) {
    mp[uf.root(c[i])].emplace(b[i]);
    ++cnt[b[i]];
  }
  int ans = 0;
  for (auto [_, boxes] : mp) ans += boxes.size() - 1;
  cout << ans << '\n';
  return 0;
}