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

vector <int> v[100005];
bool a[100005];
int n,nr;
long long m, i, p, b;

void DFS(int x)
{
    a[x] = true;
	
    for(i=0;i<v[x].size();i++)
        if (a[v[x][i]]==false)
            DFS(v[x][i]);	
}

int main()
{
	ifstream f("dfs.in");
	ofstream h("dfs.out");
	f>>n>>m;
	for (i=1; i<=m; i++)
	{
		f>>p>>b;
		v[p].push_back(b);
	}
	for (i=0;i<n;i++)
        if (a[i]==false)
        {
            DFS(i);
            nr=nr+1;
        }
	h<<nr<<'\n';
	
	
	f.close();
	h.close();
	return 0;
}