#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");
vector <int> G[100005];
int viz[100005],n,m,x,y;
long long cont;
void dfs(int nod)
{
    viz[nod]=1;
    for(auto v:G[nod])
    {
        if(!viz[v])
        {
            dfs(v);
        }
    }
}
int main()
{
    in>>n>>m;
    for(int i=1;i<=m;i++)
    {
        in>>x>>y;
        G[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
    {
        if(!viz[i])
        {
            dfs(i);
            cont++;
        }
    }
    out<<cont;
    return 0;
}