#include <vector>
#include <iostream>
#include <cmath>
#include <queue>
#include <iomanip>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define rep(i,a,b) for(auto i=(a); i<(b); ++i)
#define REP(i,n) rep(i,0,n)
#define all(v) (v).begin(), (v).end()
#define rs resize
#define DBG(x) cerr << __LINE__ << ": " << #x << " = " << (x) << endl

const ld PI = acos(-1.0);
template<class T> using min_queue =
priority_queue<T, vector<T>, greater<T>>;
template<class T> int sz(const T &x) {
    return (int) x.size(); // copy the ampersand(&)!
}

template<class T> ostream& operator<<(ostream &os, vector<T> &v) {
    os << "\n[";
    for(T &x : v) os << x << ',';
    return os << "]\n";
}

struct pairhash {
    public:
    template<typename T1, typename T2>
    size_t operator()(const pair<T1, T2> &p) const {
        size_t lhs = hash<T1>()(p.x);
        size_t rhs = hash<T2>()(p.y);
        return lhs ^ (rhs+0x9e3779b9+(lhs<<6)+(lhs>>2));
    }
};

struct SCC {
	int n, age=0, ncomps=0; vvi adj, comps;
	vi tidx, lnk, cnr, st; vector<bool> vis;
	SCC(vvi &_adj) : n(_adj.size()), adj(_adj),
			tidx(n, 0), lnk(n), cnr(n), vis(n, false) {
		for (ll i = 0; i < n; i++) {
			if (!tidx[i]) dfs(i);
		}
	}

	void dfs(int v) {
		tidx[v] = lnk[v] = ++ age;
		vis[v] = true; st.pb(v);
		for (int w : adj[v]) {
			if (!tidx[w])
				dfs(w), lnk[v] = min(lnk[v], lnk[w]);
			else if (vis[w]) lnk[v] = min(lnk[v], tidx[w]);
		}
		if (lnk[v] != tidx[v]) return;
		comps.pb(vi());
		int w;
		do {
			vis[w = st.back()] = false; cnr[w] = ncomps;
			comps.back().pb(w);
			st.pop_back();
		} while (w != v);
		ncomps++;
	}
};

void run() {
	ll n, m;
	cin >> n >> m;

	vvi adj(n);
	for (ll i = 0; i < m; i++) {
		ll a,b;
		cin >> a >> b;
		a--; b--;
		adj[a].pb(b);
	}
	SCC S(adj);
	vector<bool> source(S.ncomps, true);
	for (ll i = 0; i < n; i++) {
		for (ll j : adj[i]) {
			if (S.cnr[i] != S.cnr[j]) source[S.cnr[j]] = false;
		}
	}
	ll res = 0;
	for (bool b : source) {
		if (b) res++;
	}
	cout << res << endl;
}

signed main() {
    // DON'T MIX "scanf" and "cin"!
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout << fixed << setprecision(20);
    run();
    return 0;
}