#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<vector<int>> E(N);
  vector<vector<int>> E2(N);
  for (int i = 0; i < M; i++){
    int U, V;
    cin >> U >> V;
    U--;
    V--;
    E[U].push_back(V);
    E2[U].push_back(V);
    E2[V].push_back(U);
  }
  int cc = 0;
  vector<int> c(N, -1);
  for (int i = 0; i < N; i++){
    if (c[i] == -1 && !E2[i].empty()){
      c[i] = cc;
      queue<int> Q;
      Q.push(i);
      while (!Q.empty()){
        int v = Q.front();
        Q.pop();
        for (int w : E2[v]){
          if (c[w] == -1){
            c[w] = c[v];
            Q.push(w);
          }
        }
      }
      cc++;
    }
  }
  vector<int> in(N, 0), out(N, 0);
  for (int i = 0; i < N; i++){
    for (int j : E[i]){
      out[i]++;
      in[j]++;
    }
  }
  vector<int> D(cc, 0);
  for (int i = 0; i < N; i++){
    if (!E2[i].empty()){
      D[c[i]] += abs(in[i] - out[i]);
    }
  }
  int ans = 0;
  for (int i = 0; i < cc; i++){
    ans += max(D[i], 2);
  }
  cout << (ans - 2) / 2 << endl;
}