#include <fstream>
#include <vector>
#include <list>

std::ifstream in ("dfs.in");
std::ofstream out("dfs.out");

int n, m;
std::vector< std::list<int> > x;
std::vector<bool> seen;

void dfs (int node)
{
    seen[node] = true;
    for (std::list<int>::iterator i=x[node].begin(); i!=x[node].end(); i++)
        if (!seen[*i]) dfs(*i);
}

int main()
{
    in >> n >> m;
    x.resize (n+1);
    seen.resize (n+1, false);

    int i, a, b;
    for (i=0; i<m; i++) {
        in >> a >> b;
        x[a].push_back(b);
    }

    int count = 0;
    for (i=1; i<=n; i++) if (!seen[i]) {
        dfs (i);
        count++;
    }

    out << count;
}