#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
#define Inf 1000000001

int main(){
	
	int n,m;
	cin>>n>>m;
	
	scc_graph S(n);
	vector<int> a(m),b(m);
	rep(i,m){
		cin>>a[i]>>b[i];
		a[i]--;b[i]--;
		S.add_edge(a[i],b[i]);
	}
	
	vector<int> pos(n);
	auto s = S.scc();
	if(s.size()==1){
		cout<<0<<endl;
		return 0;
	}
	rep(i,s.size()){
		rep(j,s[i].size()){
			pos[s[i][j]] = i;
		}
	}
	
	vector<int> x(s.size()),y(s.size());
	
	rep(i,m){
		int X = pos[a[i]],Y = pos[b[i]];
		if(X==Y)continue;
		x[X]++;
		y[Y]++;
	}
	
	int ans = 0;
	
	{
		int sum = 0;
		rep(i,x.size())if(x[i]==0)sum ++;
		ans = max(ans,sum);
	}
	{
		int sum = 0;
		rep(i,y.size())if(y[i]==0)sum ++;
		ans = max(ans,sum);
	}
	
	cout<<ans<<endl;
	
	
	return 0;
}