#include <bits/stdc++.h>

using namespace std;

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

vector <int> v[100000];

int n, m, ct, valid[100000];

void Verf(int i)
{
    valid[i] = 1;

    if(!v[i].empty())
    {
        for(int j = 0; j < v[i].size(); j++)
            Verf(v[i][j]);

    }

}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);


    }

    for(int i = 1; i <= n; i++)
    {
        if(valid[i] == 0)
        {
            ct++;
            Verf(i);
        }
    }
    fout << ct;
    return 0;
}