#include <fstream>
#include <vector>
#include <bitset>
#include <string.h>
#define Nmax 100099
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");

int N,M,sol,Plus[Nmax],Minus[Nmax];
vector < int > Graph[Nmax],GT[Nmax],Comp[Nmax];


inline void ReadInput()
{
    f>>N>>M;
    for(int i=1;i<=M;++i)
    {
        int x,y;
        f>>x>>y;
        Graph[x].push_back(y);
        GT[y].push_back(x);
    }
}

void DFS_PLUS(int nod)
{
    Plus[nod]=sol;
    vector < int > :: iterator it;
    for(it=Graph[nod].begin();it!=Graph[nod].end();++it)
        if(!Plus[*it])DFS_PLUS(*it);
}

void DFS_MINUS(int nod)
{
    Minus[nod]=sol;
    if(Plus[nod]==sol)Comp[sol].push_back(nod);

    vector < int > :: iterator it;
    for(it=GT[nod].begin();it!=GT[nod].end();++it)
        if(!Minus[*it])DFS_MINUS(*it);
}

int main()
{
    ReadInput();
    for(int i=1;i<=N;++i)
        if(!Plus[i] || (Plus[i] && Plus[i]!=Minus[i]))
        {
            ++sol;
            DFS_PLUS(i);
            DFS_MINUS(i);
        }
    g<<sol<<'\n';

    f.close();g.close();
    return 0;
}