//
//  main.cpp
//  Dfs
//
//  Created by Darius Buhai on 24/11/2018.
//  Copyright © 2018 Darius Buhai. All rights reserved.
//

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

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

int n,m, viz[100001];
vector<int> a[100001];

void read()
{
    fin>>n>>m;
    int x,y;
    for(int i=0;i<m;i++){
        fin>>x>>y;
        a[x].push_back(y);
    }
}

void dfs(int x)
{
    for(auto i:a[x]){
        viz[i] = 1;
        dfs(i);
    }
}

int main() {
    read();
    int cc = 0;
    for(int i=0;i<n;i++)
    {
        if(!viz[i+1]){
            dfs(i+1);
            cc++;
        }
        
    }
    fout<<cc;
    return 0;
}