#include <fstream>
#include <vector>

using graph_t = std::vector<std::vector<int>>;

void dfs(int u, std::vector<bool> &seen, const graph_t &G)
{
    seen[u] = true;

    for (auto v : G[u])
        if (!seen[v])
        {
            dfs(v, seen, G);
        }
}

int solve(const graph_t &G)
{
    std::vector<bool> seen(G.size(), false);

    int c = 0;
    for (int u = 0; u < G.size(); u++)
        if (!seen[u])
        {
            c++;
            dfs(u, seen, G);
        }

    return c;
}

graph_t read();
void write(int c);

int main()
{
    auto G = read();
    auto c = solve(G);
    write(c);

    return 0;
}

graph_t read()
{
    std::ifstream fin("dfs.in");

    int n, m, u, v;
    fin >> n >> m;

    graph_t G(n);

    while (fin >> u >> v)
    {
        u--, v--;
        G[u].push_back(v);
    }

    return G;
}

void write(int c)
{
    std::ofstream fout("dfs.out");

    fout << c << "\n";
}