#include <bits/stdc++.h>

using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");

int n, m, s;
int x, y;

void dfs(int node, vector<bool> &vis, vector<vector<int>> &adj) {
    vis[node] = true;

    for (auto it : adj[node]) {
        if (vis[it] == false) {
            dfs(it, vis, adj);
        }
    }
}

int main() {
    in >> n >> m;
    vector<vector<int>> adj(n + 1, vector<int>());

    for (int i = 1; i <= m; i++) {
        in >> x >> y;
        adj[x].push_back(y);
    }

    vector<bool> vis(n + 1, false);
    int cnt = 0;

    for (int i = 1; i <= n; i++) {
        if (vis[i] == false) {
            cnt++;
            dfs(i, vis, adj);
        }
    }

    out << cnt << '\n';
    return 0;
}