#include <fstream>
#define fisier "dfs"
std::ifstream in(fisier ".in");
std::ofstream out(fisier ".out");
const int N = 100001;
#include <vector>
std::vector<int> L[N];
#include <bitset>
std::bitset<N> E;
bool dfs(int t)
{
    if (E[t])
        return false;
    E[t] = true;
    for (int f: L[t])
        dfs(f);
    return true;
}
int main()
{
    int n, m, s = 0;
    in >> n >> m;
    while (m--)
    {
        int a, b;
        in >> a >> b;
        L[a].push_back(b);
    }
    for (int i = 1; i <= n; i++)
        s += dfs(i);
    out << s;
}