#include <fstream>
#include <vector>
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
vector <int> v[100005];
int n, m, viz[100005];
void DFS(int nod)
{
	viz[nod] = 1;
	for (int i = 0; i < v[nod].size(); i++)
		if (!viz[v[nod][i]])
			DFS(v[nod][i]);
}
int main()
{
	f >> n >> m;
	while (m--)
	{
		int x, y;
		f >> x >> y;
		v[x].push_back(y);
	}
	int nr_c = 0;
	int ok = 1;
	while(ok)
	{
		ok = 0;
		for (int i = 1; i <= n && !ok; i++)
			if (!viz[i])
			{
				ok = 1;
				nr_c++;
				DFS(i);
			}
	}
	g << nr_c;
}