//#include <atcoder/all>
//using namespace atcoder;
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n) for(int i=0; i<n; i++)
#define REPR(i, n) for(int i=n-1; i>=0; i--)
#define FOR(i, m, n) for(int i=m; i<n; i++)
#define ALL(v) v.begin(), v.end()
#define bit(n) (1LL<<(n))
#define FIX(d) fixed << setprecision(d)
#define MAT(tp) vector<vector<tp>>
using P = pair<int, int>;
using LP = pair<ll, ll>;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const int INF = 1e9;
const ll LINF = (1LL<<60);

struct UnionFind {
  vector<int> par, sz;
  UnionFind(int n) : par(n, -1), sz(n, 1) { }
  void init(int n) { par.assign(n, -1), sz.assign(n, 1); }
   
  int root(int x) {
    if (par[x]==-1) return x;
    else return par[x] = root(par[x]);
  }
    
  bool issame(int x, int y) {
    return root(x) == root(y);
  }
    
  bool merge(int x, int y) {
    x = root(x); y = root(y);
    if (x == y) return false;
    if (sz[x] < sz[y]) swap(x, y); // merge technique
    sz[x] += sz[y];
    par[y] = x;
    return true;
  }
    
  int size(int x) {
    return sz[root(x)];
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n,m;
  cin >> n >> m;
  map<int, vector<int>> mp;
  REP(i,n){
    int b,c;
    cin >> b >> c;
    b--;
    mp[c].push_back(b);
  }

  UnionFind uf(m);
  for(auto [col, box]: mp){
    FOR(i,1,box.size()){
      uf.merge(box[0], box[i]);
    }
  }

  int ans = 0;
  REP(i,m) if(uf.root(i)==i) ans += uf.size(i)-1;
  cout << ans << endl;
  return 0;
}