#include<fstream>
#include<vector>
using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");
vector<vector<int> > v;
int f[100001];
int c[100001];
int s[100001];
long long m,i,j;
int x,y,n,ti,nr,b;

void df(int i, int & b)
{
	c[i]=1;
	
	s[i]=++ti;
	if(!v[i].empty())
		for(j=0;j<v[i].size();j++)
			{if(!c[v[i][j]])
				df(v[i][j],b);
			else
				b=1;
			}
	c[i]=2;
	f[i]=++ti;
}
int main ()
{
	in>>n>>m;
	v.resize(100001);
	for(i=1;i<=m;i++)
	{
		in>>x>>y;
		v[x].push_back(y);
	}
	
	for(i=1;i<=n;i++)
		if(!c[i])
			{b=0;
				df(i,b);
				if(!b)nr++;
			}
		
	out<<nr;
	return 0;
}