#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

struct DSU
{
	int n;
	VI p, sz;
	
	DSU(int _n = 0) 
	{
		n = _n;
		p.resize(n);
		iota(ALL(p), 0);
		sz.assign(n, 1);
	}
	int find(int v)
	{
		if (v == p[v])
			return v;
		return p[v] = find(p[v]);
	}
	bool unite(int u, int v)
	{
		u = find(u);
		v = find(v);
		if (u == v) 
			return false;
		if (sz[u] > sz[v])
			swap(u, v);
		p[u] = v;
		sz[v] += sz[u];
		return true;
	}
};

const int N = 100'447;
int in[N];
int out[N];
VI g[N];
VI gr[N];
bool used[N];
int col[N];
VI tps;

void dfs1(int v)
{
	used[v] = 1;
	for (auto to : g[v])
		if (!used[to])
			dfs1(to);
	tps.PB(v);
}

void dfs2(int v, int c)
{
	used[v] = 1;
	col[v] = c;
	for (auto to : gr[v])
		if (!used[to])
			dfs2(to, c);
}


int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int n, m;
	cin >> n >> m;
	DSU d(n);
	vector<PII> edges(m);
	FOR (i, 0, m)
	{
		int a, b;
		cin >> a >> b;
		a--, b--;
		edges[i] = {a, b};
		g[a].PB(b);
		gr[b].PB(a);
	}
	
	FOR (i, 0, n)
		if (!used[i])
			dfs1(i);
	reverse(ALL(tps));
	int c = 0;
	fill(used, used + n, false);
	for (auto v : tps)
		if (!used[v])
			dfs2(v, c++);
	
	for (auto [a, b] : edges)
	{
		if (col[a] != col[b])
		{
			out[col[a]]++;
			in[col[b]]++;
		}
		d.unite(col[a], col[b]);
	}
	if (c == 1)
	{
		cout << 0 << '\n';
		return 0;
	}
	//set<int> s;
	//FOR (i, 0, c)
	//	s.insert(d.find(i));
	//int sz = SZ(s);
	//int ans = 0;
	//int x = 0;
	//s.clear();
	//FOR (i, 0, c)
	//{
	//	ans += out[i] == 0;
	//	if (in[i] == 0)
	//		s.insert(d.find(i));
	//	x += in[i] == 0;
	//}
	//ans += x + sz - SZ(s);
	//if (x == 1)
	//	ans--;
	//cout << ans << '\n';
	int ans = 0;
	FOR (i, 0, c)
	{
		ans += out[i] == 0;
		ans += in[i] == 0;
	}
	cout << ans - 1 << '\n';
	
	return 0;
}