#include<vector>
#include<fstream>
using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

#define MAXN 100003

vector<int> G[MAXN];
bool v[MAXN];
int n,m;
int nr;

int read()
{
	f>>n;
	f>>m;
	int x,y;

	for(int i=1;i<=m;i++)
	{
		f>>x;
		f>>y;
		G[x].push_back(y);
	}

	return 0;
}

int dfs(int nod)
{
	v[nod] = true;

	for(int i=1, length = G[nod].size(); i<=length; i++)
	{
		if( v[ G[nod][i] ] != true )
		{
			dfs( G[nod][i] );
		}
	}
	
	return 0;

}

int write()
{
	g<<nr;
	
	return 0;
}

int main()
{	
	read();

	// Solve
	for(int i=1;i<=n;i++)
	{
		if(v[i] != true)
		{
			nr++;
			dfs(i);
		}
	}

	write();

	return 0; 
}