#include<bits/stdc++.h>
using namespace std;
const int N = 4e5+10;
int n,m;
int fa[N];
struct ball{
	int b,c;
}balls[N];
int find(int x){
	if(fa[x] == x){
		return x;
	}return fa[x] = find(fa[x]);
}
void unite(int x,int y){
	int nx = find(x),ny = find(y);
	if(nx != ny){
		fa[ny] = nx;
	}
}

signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin>>n>>m;
	for(int i = 1;i<=m+n;i++){
		fa[i] = i;
	}
	unordered_set<int> boxst;
	for(int i = 1;i<=n;i++){
		cin>>balls[i].b>>balls[i].c;
		int box = balls[i].b;
		int color = balls[i].c + m;
		boxst.insert(box);
		unite(box,color);
	}
	unordered_set<int> kuai;
	for(int i = 1;i<=n;i++){
		int box= balls[i].b;
		int color = balls[i].c + m;
		kuai.insert(find(box));
		kuai.insert(find(color));
	}
	int ans = boxst.size() - kuai.size();
	cout<<ans;
	return 0;
}