#include <bits/stdc++.h>

using namespace std;

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

vector<int> graf[100005];
int viz[100005];

int dfs(int nod)
{
	viz[nod]=1;
	for(int i=0;i<graf[nod].size();i++)
	{
		if(!viz[graf[nod][i]])
			dfs(graf[nod][i]);

	}
}
int main()
{
	int n,m;
	in>>n>>m;
	for(int i=1;i<=m;i++)
	{
		int x,y;
		in>>x>>y;
		graf[x].push_back(y);
	}
	int ans=0;
	for(int i=1;i<=n;i++)
	{
		if(viz[i]==0)
		{
			dfs(i);
			ans++;
		}
	}
	out<<ans;
	return 0;
}