//#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace::std;
//struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}} __init;
__attribute__((constructor))
void init(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(15);
}
// random_device rd;
// mt19937 mt(rd());
// #include <boost/numeric/interval.hpp>
// #include <boost/numeric/interval/io.hpp>
// #include <boost/intrusive/rbtree.hpp>
// #include <boost/dynamic_bitset.hpp>
// #include <boost/geometry.hpp>
// #include <boost/geometry/geometries/linestring.hpp>
// #include <boost/geometry/geometries/polygon.hpp>
// #include <boost/geometry/geometries/point_xy.hpp>
// #include <boost/math/tools/minima.hpp>
// using boost::math::tools::brent_find_minima;
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// typedef mp::number<mp::cpp_dec_float<256>> cdouble;
// typedef mp::cpp_int cint;

#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds;
template<typename T=long long>using pbds=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename T=long long>using pbds_map=tree<T,T,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename T=long long>using pqueue =__gnu_pbds::priority_queue<T, less<T>,rc_binomial_heap_tag>;
typedef long long lint;
typedef long long ll;
typedef long double ldouble;
typedef vector<lint> vec;
typedef vector<vector<lint>> mat;
typedef vector<vector<vector<lint>>> mat3;
typedef vector<double> dvec;
typedef vector<vector<double>> dmat;
typedef vector<vector<vector<double>>> dmat3;
typedef vector<string> svec;
typedef vector<vector<string>> smat;
typedef vector<vector<vector<string>>> smat3;
typedef vector<pair<lint,lint>> pvec;
typedef vector<vector<pair<lint,lint>>> pmat;
typedef vector<vector<vector<pair<lint,lint>>>> pmat3;
#define rep(i, n) for(lint i = 0; i < (lint)(n); i++)
#define irep(i) for(lint i = 0;; i++)
#define irep1(i) for(lint i = 1;; i++)
#define irep2(i) for(lint i = 2;; i++)
#define rrep(i, n) for(lint i = (lint)(n-1); i >-1; i--)
#define rrepi(i,a,b) for(lint i = (lint)(b-1); i >a-1; i--)
#define repi(i,a,b) for(lint i=lint(a);i<lint(b);i++)
#define rep2(i,a,b,c) for(lint i=lint(a);i>lint(b);i+=c)
#define all(x) (x).begin(),(x).end()
#define PI 3.141592653589793
#define dist(x1,y1,x2,y2) (pow(pow(x2-x1,2)+pow(y2-y1,2),0.5))
#define output(v) do{bool f=0;for(auto i:v){cout<<(f?" ":"");if(i>INF/2)cout<<"INF";else cout<<i;f=1;}cout<<"\n";}while(0);
#define output2(v) for(auto j:v)output(j);
#define _output(v) do{bool f=0;rep(i,v.size()){cout<<(f?" ":"");if(v[i]>INF/2)cout<<"INF";else cout<<v[i];f=1;}cout<<"\n";}while(0)
#define _output2(v) rep(j,v.size()){_output(v[j]);}
#define input(a,n) lint n;cin>>n;vector<lint>a(n);rep(i,n)cin>>a[i];
#define SUM(v) accumulate(all(v),0LL)
#define INF (1LL<<60)
#define IINF (1<<30)
#define EPS (1e-10)
#define LINF 9223372036854775807
#define MOD 998244353LL
#define endl "\n"
template<typename T=lint>T in(){return *istream_iterator<T>(cin);}
inline lint gcd(lint a,lint b){return b?gcd(b,a%b):a;}
template<typename T=lint>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
template<typename T=lint>inline T add(T a,T b){return a+b;}
template<typename T=lint>inline T minq(T a,T b){return min(a,b);}
inline bool chmin(auto& s,const auto& t){bool res=s>t;s=min(s,t);return res;}
inline bool chmax(auto& s,const auto& t){bool res=s<t;s=max(s,t);return res;}
vector<lint> dx={-1,1,0,0,1,1,-1,-1};
vector<lint> dy={0,0,-1,1,1,-1,1,-1};



// template<typename T,typename E>
// struct RBST{
// 	struct node{
// 		int cnt=1,l=-1,r=-1;
// 		T key;E val;
// 		node(){}
// 		node(T key,E val):key(key),val(val){}
// 	};
// 	vector<node> v;
// 	RBST(){
// 	}
// 	int root=1;
// 	int count(int idx){return idx==-1?0:v[idx].cnt;}
// 	int update(int idx){
// 		if(idx!=-1)v[idx].cnt=1+count(v[idx].l)+count(v[idx].r);
// 		return idx;
// 	}
// 	private:
// 	inline int merge(int l,int r){
//         if(l==-1||r==-1)return l==-1?r:l;
//         if((unsigned long)count(v[l])>rnd()%(unsigned long)(count(v[l])+count(v[r]))){
//             v[l].r=merge(v[l].r,r);
//             return update(l);
//         }else{
//             v[r].l=merge(l,v[r].l);
//             return update(r);
//         }
//     }
// 	inline pair<int,int> split(int t,int k){
//         if(t==-1)return make_pair(-1,-1);
//         if(k<=count(v[t].l)){
//             auto s=split(v[t].l,k);
//             v[t].l=s.second;
//             return make_pair(s.first,update(t));
//         }else{
//             auto s=split(v[t].r,k-count(v[t].l)-1);
//             v[t].r=s.first;
//             return make_pair(update(t),s.second);
//         }
//     }
// 	inline unsigned long rnd() {
//         static unsigned long x=123456789, y=362436069, z=521288629, w=88675123;
//         unsigned long t=(x^(x<<11));
//         x=y; y=z; z=w;
//         return ( w=(w^(w>>19))^(t^(t>>8)) );
//     }
// };
template< typename T >
struct edge {
  int src, to;
  T cost;

  edge(int to, T cost) : src(-1), to(to), cost(cost) {}

  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  edge &operator=(const int &x) {
    to = x;
    return *this;
  }

  operator int() const { return to; }
};

template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedGraph = vector< Edges< T > >;
using UnWeightedGraph = vector< vector< int > >;
template< typename T >
using Matrix = vector< vector< T > >;

template< typename G >
struct StronglyConnectedComponents {
  const G &g;
  UnWeightedGraph gg, rg;
  vector< int > comp, order, used;

  StronglyConnectedComponents(G &g) : g(g), gg(g.size()), rg(g.size()), comp(g.size(), -1), used(g.size()) {
    for(int i = 0; i < g.size(); i++) {
      for(auto e : g[i]) {
        gg[i].emplace_back((int) e);
        rg[(int) e].emplace_back(i);
      }
    }
  }

  int operator[](int k) {
    return comp[k];
  }

  void dfs(int idx) {
    if(used[idx]) return;
    used[idx] = true;
    for(int to : gg[idx]) dfs(to);
    order.push_back(idx);
  }

  void rdfs(int idx, int cnt) {
    if(comp[idx] != -1) return;
    comp[idx] = cnt;
    for(int to : rg[idx]) rdfs(to, cnt);
  }

  void build(UnWeightedGraph &t) {
    for(int i = 0; i < gg.size(); i++) dfs(i);
    reverse(begin(order), end(order));
    int ptr = 0;
    for(int i : order) if(comp[i] == -1) rdfs(i, ptr), ptr++;

    t.resize(ptr);
    for(int i = 0; i < g.size(); i++) {
      for(auto &to : g[i]) {
        int x = comp[i], y = comp[to];
        if(x == y) continue;
        t[x].push_back(y);
      }
    }
  }
};

struct UF{
    public:
    vector<lint> par;
    vector<lint> rank;
    lint _s;
    UF(lint size){
        _s=size;
        par.resize(size);
        rep(i,size)par[i]=i;
        rank.resize(size,0);
    }
    bool unite(lint x,lint y){
        x=root(x);y=root(y);
        if(x==y)return false;
        if(rank[x]<rank[y])swap(x,y);
        if(rank[x]==rank[y])rank[x]++;
        par[y]=x;
        _s--;
        return true;
    }
    lint root(lint x){
        while(x!=par[x]){
            x=par[x]=par[par[x]];
        }
        return x;
    }
    bool same(lint x, lint y) {
        return root(x) == root(y);
    }
    lint size(){
        return _s;
    }
};
struct WUF{
    public:
    vector<lint> par;
    vector<lint> rank;
    vector<lint> _w;
    lint _s;
    WUF(lint size){
        _s=size;
        par.resize(size);
        rep(i,size)par[i]=i;
        rank.resize(size,0);
        _w.resize(size,0);
    }
    bool unite(lint x,lint y,lint w){
        w+=weight(x);
        w-=weight(y);
        x=root(x);y=root(y);
        if(x==y)return false;
        if(rank[x]<rank[y]){swap(x,y);w=-w;}
        if(rank[x]==rank[y])rank[x]++;
        par[y]=x;
        _s--;
        _w[y] = w;
        return true;
    }
    lint root(lint x){
        if(par[x] == x) {
            return x;
        }else {
            lint r = root(par[x]);
            _w[x] += _w[par[x]];
            return par[x] = r;
        }
    }
    bool same(lint x, lint y) {
        return root(x) == root(y);
    }
    lint size(){
        return _s;
    }
    lint weight(lint x){
        root(x);
        return _w[x];
    }
    lint diff(lint x,lint y){
        return weight(y)-weight(x);
    }
};

int main(){
    lint n,m;
    cin>>n>>m;
    UnWeightedGraph g(n), buff;
    rep(i,m){
        int x,y;
        cin>>x>>y;
        g[x].push_back(y);
    }
    StronglyConnectedComponents< UnWeightedGraph > scc(g);
    scc.build(buff);
    lint a=0,b=0;
	if(buff.size()==1){
		cout<<0<<endl;
		return 0;
	}
    rep(i,buff.size()){
     	if(buff[i].size()==0)a++;
    }
	set<lint>s;
	rep(i,buff.size())s.insert(i);
	rep(i,buff.size())rep(j,buff[i].size()){
		s.erase(buff[i][j]);
	}
	for(auto d:s){
		if(buff[d].size()==0)b++;
	}
	cout<<max(a,(lint)s.size())<<endl;
}


Measured memory_bytes: 7356