#include <iostream>
#include <vector>
#include <fstream>
#define nmax 100001
using namespace std;

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

int n,m;
vector<int> la[nmax];
bool viz[nmax];

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

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