#include <iostream>
#include <fstream>
#include <queue>
#include <vector>

using namespace std;

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

#define nmax 100005

int n,m,S,x,y,viz[nmax],dist[nmax],comp_conex=0;

vector <int> v[nmax];

queue <int> coada;

void BFS(int nod)
{
    int k;
    viz[nod]=1;
    coada.push(nod);
    while(!coada.empty())
    {
        k=coada.front();
        vector <int> ::iterator it;
        for(it=v[k].begin();it!=v[k].end();it++)
        {
            if(!viz[*it])
            {
                viz[*it]=1;
                dist[*it]=dist[k]+1;
                coada.push(*it);
            }
        }
        coada.pop();
    }
}

int main()
{
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
    {
        if(!viz[i])
        {
            BFS(i);
            comp_conex++;
        }
    }
    fout<<comp_conex<<'\n';
}