#include <fstream>
#include <vector>
#define NMax 100005
using namespace std;

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

vector<int> G[NMax],GT[NMax];
int N,M,NrCTC,Use[NMax];

void Read()
{
    fin>>N>>M;
    for(int i=1;i<=M;i++)
        {
        int x,y;
        fin>>x>>y;
        G[x].push_back(y);
        GT[y].push_back(x);
        }
}

void DFSP(int Nod)
{
    Use[Nod] = 1;
    for(unsigned int i=0; i<G[Nod].size();i++)
    {
        int Vecin = G[Nod][i];
        if(!Use[Vecin])
            DFSP(Vecin);
    }
}

void DFSM(int Nod)
{
    Use[Nod] = 2;
    for(unsigned int i=0; i<GT[Nod].size();i++)
    {
        int Vecin = GT[Nod][i];
        if(Use[Vecin]==1)
            DFSM(Vecin);
    }
}


void Reset()
{
    for(int i=1;i<=N;i++)
        if(Use[i]==1)
            Use[i]=0;
}

void Solve()
{
    for(int i=1;i<=N;i++)
    {
        if(!Use[i])
        {
            DFSP(i);
            NrCTC++;
            DFSM(i);
            Reset();
        }
    }
}

void Print()
{
    fout<<NrCTC<<"\n";
}

int main()
{
    Read();
    Solve();
    Print();
    return 0;
}