#include <bits/stdc++.h>
#define NMAX 100005
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");

vector < int > v[NMAX];
int n,m,a,b,rasp;
bool verif[NMAX];

void bfs(int nod)
{
    int lungime=v[nod].size();
    for(int i=0;i<lungime;i++)
    {
        if(verif[v[nod][i]]==0)
        {
            verif[v[nod][i]]=1;
            bfs(v[nod][i]);
        }
    }
}

int main()
{
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>a>>b;
        if(a!=b)v[a].push_back(b);
    }
    for(int i=1;i<=n;i++)
    {
        if(verif[i]==0)
        {
            verif[i]=1;
            bfs(i);
            rasp++;
        }
    }
    fout<<rasp;
}