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

using namespace std;

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

int n,m,viz[100010],nc;
vector <int> g[100010];

void dfs(int nod)
{
    viz[nod]=nc;
    int i;
    for (i=0;i<g[nod].size();i++)
        if (viz[g[nod][i]]==0)
            dfs(g[nod][i]);
}

int main()
{
    int i,j,x,y;
    fin>>n>>m;
    for (i=1;i<=m;i++)
    {
        fin>>x>>y;
        g[x].push_back(y);
    }
    for (i=1;i<=n;i++)
        if (viz[i]==0)
        {
            nc++;
            dfs(i);
        }
    fout<<nc;
    return 0;
}