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

using namespace std;

ifstream cin("dfs.in");
ofstream cout("dfs.out");

vector<int> A[100001];

int n,m,s,nr;
int viz[100001];

void DFS(int v)
{
    viz[v]=1;
    for (vector<int>::iterator it=A[v].begin();it!=A[v].end();it++)
    {
        int nod=*it;
        if (!viz[nod])
        {
            DFS(nod);
        }
    }
}

int main()
{
    cin >> n >> m;
    for (int i=1; i<=m; i++)
    {
        int x,y;
        cin >> x >> y;
        A[x].push_back(y);
    }
    for (int i=1;i<=n;i++)
    {
        if (viz[i]==0)
        {
            nr++;
            DFS(i);
        }
    }
    cout << nr;
}