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

#define NMAX 100000

using namespace std;

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

vector <int> v[NMAX],viz;

void dfs(int k)
{
    viz[k]=1;
    for(auto x:v[k])
        if(!viz[x])
            dfs(x);
}

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