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

using namespace std;

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

queue <int> q;

const int nmax=100000;

vector <int> g[nmax+1];

int d[nmax+1];

int main(){
    int n,m;
    fin>>n>>m;
    int sol=0;
    for(int i=1;i<=m;i++){
        int x,y;
        fin>>x>>y;
        g[x].push_back(y);
    }
    for(int s=1;s<=n;s++){
        if(d[s]==0){
            q.push(s);
            d[s]=1;
            while(q.empty()==0){
                int x=q.front();
                q.pop();
                for(int i=0;i<int(g[x].size());i++){
                    int xn=g[x][i];
                    if(d[xn]==0){
                        q.push(xn);
                        d[xn]=d[x]+1;
                    }
                }
            }
            sol++;
        }
    }
    fout<<sol;
    fout<<"\n";
    return 0;
}