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

using namespace std;

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

queue <int> q;

int viz[100005];
vector <int> v[100005];

int n,m,ans;

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

int a,b;

int main()
{
    fin>>n>>m;
    for(int i=1;i<=m;i++){
        fin>>a>>b;
        v[a].push_back(b);
    }
    for(int i=1;i<=n;i++){
        if(viz[i]==0){
            dfs(i);
            ans++;
        }
    }
    fout<<ans<<'\n';
    return 0;
}