#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int n, m;
vector<vector<int>> g, rg;
vector<int> post, rs;
vector<bool> done;

void dfs1(int i){
    if (done[i]) return;
    done[i] = true;
    for (int j : g[i]) dfs1(j);
    post.push_back(i);
}

bool dfs2(int r, int i){
    if (rs[i] >= 0) return rs[i] != r;
    rs[i] = r;
    bool in = false;
    for (int j : rg[i]) in = dfs2(r, j) || in;
    return in;
}

int main(){
    cin >> n >> m;
    g = vector<vector<int>>(n);
    rg = vector<vector<int>>(n);

    for (int i = 0; i < m; ++i){
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        g[a].push_back(b);
        rg[b].push_back(a);
    }

    post = vector<int>(n);
    done = vector<bool>(n);
    for (int i = 0; i < n; ++i) dfs1(i);

    reverse(post.begin(), post.end());
    rs = vector<int>(n, -1);
    int count = 0;
    for (int i : post) if (rs[i] == -1) if (!dfs2(i, i)) ++count;
    cout << count << endl;
}