#include <fstream>
#include <vector>
#include <stack>
#include <iostream>
using namespace std;

vector< vector<unsigned int> > Graph;
vector<int> Visited;
int n, m, comp;

void Read(){
    ifstream f ("dfs.in");
    int x, y;

    f >> n >> m;
    Graph.resize(n+1);
    for(int i = 1; i <= m; ++i){
        f >> x >> y;
        Graph[x].push_back(y);
    }
    f.close();
}

void Dfs(){
    stack<unsigned int> St;
    Visited.resize(n+88, -1);
    for(int i = 1; i <= n; ++i){
        vector<unsigned int>::iterator it;

        if(Visited[i] == -1){
            St.push(i);
            comp++;
            while(!St.empty()){
                int x = St.top();
                for(it = Graph[x].begin(); it != Graph[x].end(); ++it){
                    if(Visited[*it] == -1){
                        St.push(*it);
                        Visited[*it] = 0;
                    }
                }
                St.pop();
            }
        }
    }
}

void Write(){
    ofstream g ("dfs.out");
    g << comp << "\n";
    g.close();
}

int main(){
    Read();
    Dfs();
    Write();
    return 0;
}