#include <bits/stdc++.h>
using namespace std;
int main(){
  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>> id(N);
  for (int i = 0; i < N; i++){
    id[c[i]].push_back(b[i]);
  }
  vector<vector<int>> E(M);
  for (int i = 0; i < N; i++){
    int cnt = id[i].size();
    for (int j = 1; j < cnt; j++){
      E[id[i][0]].push_back(id[i][j]);
      E[id[i][j]].push_back(id[i][0]);
    }
  }
  int cnt = 0;
  vector<bool> used(M, false);
  for (int i = 0; i < M; i++){
    if (!used[i]){
      used[i] = true;
      cnt++;
      queue<int> Q;
      Q.push(i);
      while (!Q.empty()){
        int v = Q.front();
        Q.pop();
        for (int w : E[v]){
          if (!used[w]){
            used[w] = true;
            Q.push(w);
          }
        }
      }
    }
  }
  cout << M - cnt << endl;
}