#include<fstream>
#include<vector>
#define MaxN 100001
using namespace std;

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

vector<int> a[MaxN];

int k,n,m,i,j,x,y;
bool viz[MaxN];

void dfs(int nod)
{	vector<int>::iterator *it
	viz[nod]=true;
	for(it=a[nod].begin();it!=a[nod].end();++it)
			if(viz[*it]==false)
				dfs(*it);
}

int main()
{	fin>>n>>m;
	for(i=1;i<=m;i++)
	{	fin>>x>>y;
		a[x].push_back(y);
	}
	for(i=1;i<=n;i++)
		if(viz[i]==false)
		{	k++;
			dfs(i);
		}
	fout<<k<<'\n';
	return 0;
}