#include <bits/stdc++.h>
using namespace std;
ifstream fin("bfs.in");
ofstream fout("bfs.out");
int N, M, S, nrcc=0;
vector <int> l[100005];
queue <int> q;
int viz[100005];
void bfs(int nod)
{
    int aux;
    q.push(nod);
    viz[nod]=1;
    while(!q.empty())
    {
        aux=q.front();
        for(auto &p : l[aux])
        {
            if(viz[p]==0)
            {
                viz[p]=viz[aux]+1;
                q.push(p);
            }
        }
        q.pop();
    }
}

int main()
{
    int x, y;
    fin >> N >> M;
    for(int i=1; i<=M; i++)
    {
        fin >> x >> y;
        l[x].push_back(y);
    }
    for(int i=1;i<=N;i++)
    {
        if(viz[i]==0)
        {
            bfs(i);
            nrcc++;
        }
    }
    fout << nrcc;
}