#include <fstream>
#include <vector>
using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

vector <int> v[100002];
int n,m,a,b,p[100002],nr;
bool viz[100002];

void DFS(int c)
{
    viz[c]=1;
    int aux = v[c].size();
    for(int i=1;i<=aux;++i)
    {
        DFS(v[c].back());
        v[c].pop_back();
    }
}
int main()
{
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        f>>a>>b;p[i]=a;
        v[a].push_back(b);
    }
    for(int i=1;i<=n;++i)
    {
        if(!viz[i])nr++,DFS(p[i]);
    }
    g<<nr<<'\n';
    return 0;
}