#include<iostream>
#include<fstream>
#include<vector>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n,m;
int con = 0;
std::vector< std::vector<int> > graph;
std::vector<bool> viz;
void dfs(int node)
{
    viz[node] = 1;
    for(int i=0;i<graph[node].size();i++)
    {
        if(viz[graph[node][i]] == 0)
        {
            dfs(graph[node][i]);
        }
    }
}
int main()
{
    fin>>n>>m;
    viz.assign(n,0);
    std::vector<int> x;
    graph.assign(n,x);
    for(int i=0;i<m;i++)
    {
        int k1,k2;
        fin>>k1>>k2;
        graph[k1-1].push_back(k2-1);
    }
    for(int i=0;i<n;i++)
    {
        if(viz[i] == 0)
        {
            con++;
            dfs(i);
        }
    }
    std::fout<<con;
}