#include <fstream>
#include <vector>

using namespace std;

ifstream cin("dfs.in");
ofstream cout("dfs.out");

void dfs(vector<vector<int>> &g, vector<bool> &viz, int start) {
    vector<int> langa = g[start];
    viz[start] = true;
    for(auto i : langa) {
        dfs(g, viz, i);
    }
}

int main()
{
    int n, m;
    cin >> n >> m;
    vector<vector<int>> g(n);
    vector<bool> viz(n, false);
    for(int i = 0; i < m; i++) {
        int x, y;
        cin >> x >> y;
        x--; y--;
        g[x].push_back(y);
    }
    int ans = 0;
    for(int i = 0; i < n; i++) {
        ans += !viz[i];
        dfs(g, viz, i);
    }
    cout << ans << "\n";
}