#include <fstream>
#include <vector>

using namespace std;

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

int n,m,i,used[100001],used2[100001],x,y,j,cont;
vector <int> nod[100001],nod2[100001],exit,ctc,comp[100001];

int dfs(int x)
{
    for(int i=0;i<nod[x].size();i++)
        if(!used[nod[x][i]])
        {
            used[nod[x][i]]=1;
            dfs(nod[x][i]);
        }
    exit.push_back(x);
}
int dfs2(int x,vector <int>& V)
{
    for(int i=0;i<nod2[x].size();i++)
        if(!used[nod2[x][i]])
        {
            used2[nod2[x][i]]=1;
            dfs2(nod2[x][i],V);
        }
    V.push_back(x);
}
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        nod[x].push_back(y);
        nod2[y].push_back(y);
    }
    for(i=1;i<=n;i++)
        if(!used[i])
            dfs(i);
    for(j=n;j>0;j--)
    {
        if(!used2[j])
            dfs2(j,ctc);
        comp[++cont]=ctc;
        ctc.erase(ctc.begin(),ctc.end());
    }
    fout<<cont<<'\n';
    return 0;
}