#include <fstream>
#include <vector>

using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

int x, y, i, j, n, m, nr;
vector <int> a[100005];
bool viz[100005];

void df(int nod)
{
    viz[nod] = 1;
    for (int i = 0; i < a[nod].size(); i++)
        if (viz[a[nod][i]] == 0)
            df(a[nod][i]);
}

int main()
{
    f >> n >> m;
    for (i = 1; i <= m; i++)
    {
        f >> x >> y;
        a[x].push_back(y);
    }
    for (i = 1; i <= n; i++)
        if (viz[i] == 0)
        {
            df(i);
            nr++;
        }
    g << nr;
    return 0;
}