/* -*- coding: utf-8 -*-
 *
 * 1390.cc:  No.1390 Get together - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;
const int MAX_M = 200000;

/* typedef */

template <const int MAX_N>
struct UFT {
  int links[MAX_N], ranks[MAX_N], sizes[MAX_N];
  UFT() {}

  void init(int n) {
    for (int i = 0; i < n; i++) links[i] = i, ranks[i] = sizes[i] = 1;
  }

  int root(int i) {
    int i0 = i;
    while (links[i0] != i0) i0 = links[i0];
    return (links[i] = i0);
  }

  int rank(int i) { return ranks[root(i)]; }
  int size(int i) { return sizes[root(i)]; }
  bool same(int i, int j) { return root(i) == root(j); }

  int merge(int i0, int i1) {
    int r0 = root(i0), r1 = root(i1), mr;
    if (r0 == r1) return r0;
    if (ranks[r0] == ranks[r1]) {
      links[r1] = r0;
      sizes[r0] += sizes[r1];
      ranks[r0]++;
      mr = r0;
    }
    else if (ranks[r0] > ranks[r1]) {
      links[r1] = r0;
      sizes[r0] += sizes[r1];
      mr = r0;
    }
    else {
      links[r0] = r1;
      sizes[r1] += sizes[r0];
      mr = r1;
    }
    return mr;
  }
};

/* global variables */

int cbs[MAX_N];
UFT<MAX_M> uft;
bool us[MAX_M], rs[MAX_M];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);

  memset(cbs, -1, sizeof(cbs));
  uft.init(m);

  for (int i = 0; i < n; i++) {
    int bi, ci;
    scanf("%d%d", &bi, &ci);
    bi--, ci--;

    us[bi] = true;
    if (cbs[ci] < 0) cbs[ci] = bi;
    else uft.merge(cbs[ci], bi);
  }

  for (int i = 0; i < n; i++)
    if (cbs[i] >= 0) rs[uft.root(cbs[i])] = true;

  int un = 0, rn = 0;
  for (int i = 0; i < m; i++) {
    if (us[i]) un++;
    if (rs[i]) rn++;
  }

  printf("%d\n", un - rn);
  return 0;
}