// g++ 1.cpp -std=c++17 -O2 -I .
#include <bits/stdc++.h>
using namespace std;

#include <atcoder/all>
using namespace atcoder;

using ll = long long;
using ld = long double;
 
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vvld = vector<vld>;
using vst = vector<string>;
using vvst = vector<vst>;
 
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define pq_big(T) priority_queue<T,vector<T>,less<T>>
#define pq_small(T) priority_queue<T,vector<T>,greater<T>>
#define all(a) a.begin(),a.end()
#define rep(i,start,end) for(ll i=start;i<(ll)(end);i++)
#define per(i,start,end) for(ll i=start;i>=(ll)(end);i--)
#define uniq(a) sort(all(a));a.erase(unique(all(a)),a.end())

#include <vector>
#include <cassert>

struct union_find_group{
  private:
  int n;
  std::vector<int> parent_size;
  // 正 親
  // 負 -1*サイズ
  std::vector<std::vector<int>> group_info;
  // group の集合情報を常に管理

  public:
  union_find_group(int sz){
    n=sz;
    parent_size.resize(n,-1);
    group_info.resize(n);
    for(int i=0;i<n;i++){
      group_info[i].emplace_back(i);
    }
  }

  int root(int i){
    assert(0<=i&&i<n);
    if(parent_size[i]<0)return i;
    return parent_size[i]=root(parent_size[i]);
  }

  int size(int i){
    return -1*parent_size[root(i)];
  }

  bool same(int i,int j){
    assert(0<=i&&i<n&&0<=j&&j<n);
    return root(i)==root(j);
  }

  int merge(int i,int j){
    int ri=root(i),rj=root(j);
    if(ri==rj)return ri;

    // |riの部分集合|>=|rj|の部分集合としたい
    if(parent_size[ri]>parent_size[rj]){
      std::swap(ri,rj);
    }

    parent_size[ri]+=parent_size[rj];
    parent_size[rj]=ri;
    for(int vartex_rj:group_info[rj]){
      group_info[ri].emplace_back(vartex_rj);
    }
    return ri;
  }

  std::vector<int> group(int i){
    int ri=root(i);
    return group_info[ri];
  }
};

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n,m;cin>>n>>m;
  union_find_group uf(n);
  vi in(n,0);
  vi out(n,0);

  rep(i,0,m){
    int u,v;cin>>u>>v;
    u--;v--;
    in[v]++;
    out[u]++;
    uf.merge(u,v);
  }

  vvi v;
  rep(i,0,n){
    if(uf.root(i)==i){
      v.emplace_back(uf.group(i));
    }
  }

  ll ans=v.size()-1;
  for(vi g:v){
    vi d;
    for(int id:g){
      d.emplace_back(in[id]-out[id]);
    }
    int d2=0;
    for(int dd:d){
      d2+=abs(dd);
    }
    
    if(d2>2)ans+=d2/2-1;
    if(g.size()==1&&d2==0)ans--;
  }

  cout<<ans<<endl;
}