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

using namespace std;

int V,E,maxi;
int visited[100001];
vector< vector<int> >graph;
void dfs(int curr,int sum)
{
    visited[curr]=1;
    for(int w=0;w<graph[curr].size();w++)
        if(!visited[graph[curr][w]])
        dfs(graph[curr][w],sum+1);



}
int main()
{
freopen("dfs.in","r",stdin);
freopen("dfs.out","w",stdout);
    cin>>V>>E;
    graph.resize(V+1);
    for(int x=0;x<E;x++)
    {
        int temp1,temp2;
        cin>>temp1>>temp2;
        graph[temp1].push_back(temp2);

    }
for(int x=1;x<=V;x++)
{
    if(!visited[x])
    {


    dfs(x,0);
    maxi++;
}}
    cout<<maxi<<endl;
    return 0;
}