#include <bits/stdc++.h>
//#include<boost/multiprecision/cpp_int.hpp>
//#include<boost/multiprecision/cpp_dec_float.hpp>
//#include <atcoder/all>
#define rep(i, a) for (int i = (int)0; i < (int)a; ++i)
#define rrep(i, a) for (int i = (int)a - 1; i >= 0; --i)
#define REP(i, a, b) for (int i = (int)a; i < (int)b; ++i)
#define RREP(i, a, b) for (int i = (int)a - 1; i >= b; --i)
#define repl(i, a) for (ll i = (ll)0; i < (ll)a; ++i)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define popcount __builtin_popcount
#define fi first
#define se second
using ll = long long;
constexpr ll mod = 1e9 + 7;
constexpr ll mod_998244353 = 998244353;
constexpr ll INF = 1LL << 60;

// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

//using lll=boost::multiprecision::cpp_int;
//using Double=boost::multiprecision::number<boost::multiprecision::cpp_dec_float<1024>>;//仮数部が1024桁
template <class T>
inline bool chmin(T &a, T b)
{
	if (a > b)
	{
		a = b;
		return true;
	}
	return false;
}
template <class T>
inline bool chmax(T &a, T b)
{
	if (a < b)
	{
		a = b;
		return true;
	}
	return false;
}

template <typename T>
T mypow(T x, T n, const T &p = -1)
{ //x^nをmodで割った余り

	if (p != -1)
	{
		x %= p;
	}
	T ret = 1;
	while (n > 0)
	{
		if (n & 1)
		{
			if (p != -1)
				ret = (ret * x) % p;
			else
				ret *= x;
		}
		if (p != -1)
			x = (x * x) % p;
		else
			x *= x;
		n >>= 1;
	}
	return ret;
}

using namespace std;
//using namespace atcoder;

struct UF{
	vector<int>par,sz;
	UF(int _n){
		par.resize(_n);
		sz.resize(_n,1);
		rep(i,_n)par[i]=i;
	}
	
	int find(int x){
		if(par[x]==x)return par[x];
		else return par[x]=find(par[x]);
	}

	void unite(int x,int y){
		x=find(x),y=find(y);
		if(x==y)return;
		if(sz[x]>sz[y]){
			sz[x]+=sz[y];
			par[y]=par[x];
		}else{
			sz[y]+=sz[x];
			par[x]=par[y];
		}
	}
	bool same(int x,int y){
		return find(x)==find(y);
	}
};
void solve()
{
	int n,m;
	cin>>n>>m;

	UF tree(n);
	vector<int>b(n),c(n);
	vector<vector<int>>box(m),color(n);
	rep(i,n){
		cin>>b[i]>>c[i],b[i]--,c[i]--;
		box[b[i]].eb(c[i]);
		color[c[i]].eb(b[i]);
	}
	rep(i,m){
		int sz=box[i].size();
		rep(j,sz-1){
			tree.unite(box[i][j],box[i][j+1]);
		}
	}
	int ans=0;
	vector<set<int>>st(n);
	rep(i,m){
		if(!box[i].empty()){
			st[tree.find(box[i][0])].emplace(i);
		}
	}
	for(auto x:st){
		if(!x.empty()){
			ans+=(int)x.size()-1;
		}
	}
	cout<<ans<<"\n";
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}