#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
const int Nmax=100000+5;
bool viz[Nmax];
vector<int>v[Nmax];
int n,m,cont=0;
void DFS(int nod)
{
    viz[nod]=1;
    for(int i=0;i<v[nod].size();++i)
    if(!viz[v[nod][i]])
        DFS(v[nod][i]);
}
int main()
{
    fin>>n>>m;
    for(int i=1,x,y;i<=m;++i)
    {
        fin>>x>>y;
        v[x].push_back(y);
    }
    //for(int i=1;i<=n;i++)
    //{
        //for(int j=0;j<v[i].size();++j)
            //fout<<v[i][j]<<" ";
    //}
    for(int i=1;i<=n;++i)
        if(viz[i]!=1 && !v[i].empty())
        {
            viz[i]=1;
            for(int j=0;j<v[i].size();++j)
            {
                viz[j]=1;
                cont++;
                DFS(j);
            }
        }
    fout<<cont;
    return 0;
}