#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	scc_graph ss(n);
	vector<int>a(m), b(m);
	rep(i, m) {
		cin >> a[i] >> b[i]; a[i]--, b[i]--;
		ss.add_edge(a[i], b[i]);
	}
	auto vv = ss.scc();
	if (1 == vv.size()) {
		cout << 0 << endl;
		return 0;
	}
	vector<int>g(n);
	int sz = vv.size();
	for (auto & v : vv) {
		auto top = v[0];
		for (auto e : v) g[e] = top;
	}
	vector<int>in(n), out(n);
	rep(i, m) {
		if (g[a[i]] == g[b[i]])continue;
		in[g[a[i]]]++;
		out[g[b[i]]]++;
	}
	int incount = 0, outcount = 0;
	rep(i, n) {
		if (in[i])incount++;
		if (out[i])outcount++;
	}
	int ans = sz - min(incount, outcount);
	cout << ans << endl;
	return 0;
}