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

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

int v[100010], N, M, S;

vector<int> G[100010];


void DFS(int S)
{

	v[S] = 1;

	for (int i = 0;i < G[S].size();++i)
		if (!v[G[S][i]])
			DFS(G[S][i]);
}

int main()
{
	in >> N >> M;

	for (int i = 1;i <= M;++i)
	{
		int x, y;
		in >> x >> y;

		G[x].push_back(y);
	}
	
	int nr = 0;

	for (int i = 1;i <= N;++i)
		if (!v[i])
		{
			++nr;
			DFS(i);
		}

	out << nr;

	return 0;


}