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

using namespace std;

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

vector<int> la[100000];
int n, m;
int vis[100000];

void dfs(int nod)
{
    vis[nod] = 1;
    for (auto& el: la[nod])
    {
        if (!vis[el])
            dfs(el);
    }
}


int main()
{
    in >> n >> m;

    for (int i = 0; i < m; i++)
    {
        int n1, n2;
        in >> n1 >> n2;
        la[n1-1].push_back(n2-1);
    }

    int nr = 0;
    for (int i = 0; i < n; i++)
    {
        if (!vis[i])
        {
            dfs(i);
            nr ++;
        }
    }

    out << nr;

    return 0;
}