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

vector <int> a[100001],b[100001];
bool v[100001];
int c[100001],i,n,m,x,y,nr,k;

void df(int x)
{
	int i;
	v[x]=1;
	for (i=0;i<a[x].size();i++)
	{
		if (v[a[x][i]]==0)
			df(a[x][i]);
	}
	c[++k]=x;
}

void df2(int x)
{
	int i;
	v[x]=1;
	for (i=0;i<b[x].size();i++)
		if (v[b[x][i]]==0)
			df2(b[x][i]);
}

int main()
{
	ifstream f("ctc.in");
	ofstream g("ctc.out");
	f >> n >> m;
	for (i=1;i<=m;i++)
	{
		f >> x >> y;
		a[x].push_back(y);
		b[y].push_back(x);
	}
	for (i=1;i<=n;i++)
		if (v[i]==0)
			df(i);
	for (i=1;i<=n;i++)
		v[i]=0;
	for (i=n;i>=1;i--)
		if (v[c[i]]==0)
		{
			nr++;
			df2(c[i]);
		}
	g << nr;
	return 0;
}