#include <fstream>
#include <iostream>
#include <vector>

std::vector < std::vector <int> > adiacenta;
std::vector < bool > vizitat;
int n, m;

void DFS(int nod)
{
	vizitat[nod] = true;
	for (int i = 0; i < adiacenta[nod].size(); i++)
	{
		if (vizitat[adiacenta[nod][i]] == false)
		{
			DFS(adiacenta[nod][i]);
		}
	}
}

int main()
{
	std::ifstream f("dfs.in");
	std::ofstream g("dfs.out");
	f >> n >> m;
	adiacenta.resize(n + 1);
	vizitat.resize(n + 1, false);
	int x, y;
	for (int i = 1; i <= m; i++)
	{
		f >> x >> y;
		adiacenta[x].push_back(y);
	}
	int contor = 0;
	for (int i = 1; i <= n; i++)
	{
		if (vizitat[i] == false)
		{
			contor++;
			DFS(i);
		}
	}
	g << contor;



	return 0;
}