/*#include<fstream>
#define NMAX 10000
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
/*
//varianta 1
int D[NMAX][NMAX],n,viz[NMAX],m,x,y;
void citire()
{
    int i,j;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        D[x][y]=1;
    }
}
void construire()
{
    int i,j,k;
    for(k=1;k<=n;k++)
        for(i=1;i<=n;i++)
            for(j=1;j<=n;j++)
                if(D[i][k] && D[k][j])
                    D[i][j]=1;
}
void rezolvare(int x)
{
    int i,j;
    for(j=1;j<=n;j++)
    {
        if(viz[j]==0)
        {
            viz[j]=1;
            fout<<j<<" ";
            for(i=1;i<=n;i++)
            {
                if(D[j][i]==1 && D[i][j]==1 && viz[i]==0)
                {
                    viz[i]=1;
                    fout<<i<<" ";
                }
            }
            fout<<"\n";
        }

    }
}

int main()
{
    citire();
    construire();
    rezolvare(1);
}*/
//varianta 3
/*
int n,m,i,nrp;
int G[NMAX][NMAX],GT[NMAX][NMAX];
int postordine[NMAX],viz[NMAX];
void citire()
{
    int x,y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        G[x][y]=1;
        GT[y][x]=1;
    }
}
void DFS(int x)
{
    int St[NMAX],k,v,y;
    St[1]=x;
    viz[x]=1;
    k=1;
    while(k)
    {
        v=St[k];
        y=0;
        for(i=1;i<=n;i++)
        {
            if(G[v][i] && viz[i]==0)
            {
                y=i;
                break;
            }
        }
        if(y==0) k--;
        else
        {
            viz[y]=1;
            St[++k]=y;
        }
    }
    postordine[++nrp]=i;
}
void DFST(int x)
{
    int St[NMAX],k,v,y;
    St[1]=x;
    viz[x]=1;
    fout<<x<<" ";
    k=1;
    while(k)
    {
        v=St[k];
        y=0;
        for(i=1;i<=n;i++)
        {
            if(GT[v][i] && viz[i]==0)
            {
                y=i;
                break;
            }
        }
        if(y==0) k--;
        else
        {
            viz[y]=1;
            fout<<y<<" ";
            St[++k]=y;
        }
    }
}

int main()
{
    citire();
    for(i=1;i<=n;i++)
    {
        if(viz[i]==0)
            DFS(i);
    }
    for(i=1;i<=n;i++)   viz[i]=0;
    for(i=nrp;i>=1;i--)
    {
        if(viz[postordine[i]]==0)
            DFST(postordine[i]);
        fout<<"\n";
    }
return 0;
}*/
#include <fstream>
#include<cstdio>
#include <vector>
#define NMAX 100002
using namespace std;
FILE *fin,*fout;
int n,m,nr,ctc;
vector <int> G[NMAX];
vector <int> Gt[NMAX];
vector <int> M[NMAX];
int use[NMAX];
int postordine[NMAX];

void cit()
{
    int i,x,y;
    fin=fopen("ctc.in","r");
    fscanf(fin,"%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        fscanf(fin,"%d%d",&x,&y);
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}

void dfs(int vf)
{
    int i,nra;
    nra=G[vf].size();
    use[vf]=1;
    for(i=0;i<nra;i++)
    {
        if(!use[G[vf][i]])
        {
            dfs(G[vf][i]);
        }
    }
    postordine[++nr]=vf;
}

void dfst(int vf)
{
    int i,nra;
    nra=Gt[vf].size();
    use[vf]=0;
    M[ctc].push_back(vf);
    for(i=0;i<nra;i++)
    {
        if(use[Gt[vf][i]])
            dfst(Gt[vf][i]);
    }
}
void afisare()
{
    int i,j,lg;
    fout=fopen("ctc.out","w");
    fprintf(fout,"%d",ctc);


}

int main()
{
    int i;
    cit();
    nr=0;
    for(i=1;i<=n;i++)
    {
        if(!use[i])
            dfs(i);
    }
    for(i=n;i>=1;i--)
    {
        if(use[postordine[i]])
        {
            dfst(postordine[i]);
            ctc++;
        }
    }
    afisare();
    return 0;
}