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

using namespace std;

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

int n, m, viz[100010], contor, x, y;

vector<int> v[100010];

void dfs(int nod)
{
    viz[nod] = 1;
    for (int i = 0; i < v[nod].size(); i++)
    {
        if (!viz[v[nod][i]])
        {
            viz[v[nod][i]] = 1;
            dfs(i);
        }
    }
}

int main()
{
    f>>n>>m;
    for (int i = 1; i <= m; i++)
    {
        f>>x>>y;
        v[x].push_back(y);
    }
    for (int i = 1; i <= n; i++)
    {
        if (!viz[i])
        {
            contor++;
            dfs(i);
        }
    }
    g<<contor;
    return 0;
}