#include <iostream>
#include <vector>
#include <queue>
#include <fstream>
#define Nmax 100001

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

vector <int> gr[Nmax];
queue <int> dr;
int n, m, nr;
int viz[Nmax];


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