#include <fstream>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
struct nod
{
    int val;
    nod *urm;
};
typedef nod *pnod;
pnod v[100003],p;
int ind[100003],lind[100003];
int s[100003],sf;
int n;
int minim(int a,int b)
{
    if(a>b)
        return b;
    return a;
}
void ad(int x,int y)
{
    p=new nod;
    p->val=y;
    p->urm=v[x]->urm;
    v[x]->urm=p;
}
int index,nr;
void tarjan(int cur)
{
    ind[cur]=index;
    lind[cur]=index;
    s[index]=cur;
    index+=1;
    pnod p;
    p=v[cur]->urm;
    while(p)
    {
        if(ind[p->val]==0)
        {
            tarjan(p->val);
            lind[cur]=minim(lind[cur],lind[p->val]);
        }

        else
        {
            lind[cur]=minim(lind[cur],ind[p->val]);
        }
        p=p->urm;
    }
    if(lind[cur]==ind[cur])
    {
        nr+=1;
    }
}
int main()
{
    int i,m,x,y;
    f>>n;
    for(i=1;i<=n;i++)
    {
        v[i]=new nod;
        v[i]->urm=0;
    }
    f>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        ad(x,y);
    }
    for(i=1;i<=n;i++)
    {
        if(ind[i]==0)
        {
            index=1;
            tarjan(i);
        }
    }
    g<<nr<<'\n';
    f.close();
    g.close();
    return 0;
}