#include<iostream>
#include<fstream>
#include<vector>
using namespace std;
int sol=0,viz[100000],t[100000],n;
vector<int>a[100000];
int nr=0;
void df(int nod){
		viz[nod]=1;
		for(int i=0;i<a[nod].size();i++)
			if(!viz[a[nod][i]])
				df(a[nod][i]);
		t[nr++]=nod;
}
void componente(){
	int i;
	for(i=1;i<=n;i++)
		if(!viz[i]){
			
			df(i);sol++;
		}

}
int main(){
	
	ifstream f("dfs.in");
	ofstream g("dfs.out");
	f>>n;
	while(!f.eof()){
		int x,y;
		f>>x>>y;
		a[x].push_back(y);
	}
	componente();
	g<<sol;
	return 0;
}