#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

struct UnionFind {
  explicit UnionFind(const int n) : data(n, -1) {}

  int root(const int ver) {
    return data[ver] < 0 ? ver : data[ver] = root(data[ver]);
  }

  bool unite(int u, int v) {
    u = root(u);
    v = root(v);
    if (u == v) return false;
    if (data[u] > data[v]) std::swap(u, v);
    data[u] += data[v];
    data[v] = u;
    return true;
  }

  bool is_same(const int u, const int v) { return root(u) == root(v); }

  int size(const int ver) { return -data[root(ver)]; }

 private:
  std::vector<int> data;
};

int main() {
  int n, m; cin >> n >> m;
  vector<int> u(m), v(m); REP(i, m) cin >> u[i] >> v[i], --u[i], --v[i];
  vector<int> deg(n, 0);
  UnionFind union_find(n);
  REP(i, m) {
    --deg[u[i]];
    ++deg[v[i]];
    union_find.unite(u[i], v[i]);
  }
  vector<int> outdeg(n, 0);
  REP(i, n) {
    if (deg[i] > 0) outdeg[union_find.root(i)] += deg[i];
  }
  vector<int> has_edge(n, false);
  REP(i, m) has_edge[union_find.root(u[i])] = true;
  int ans = 0;
  REP(i, n) {
    if (union_find.root(i) == i && has_edge[i]) {
      ans += max(outdeg[i], 1);
    }
  }
  cout << ans - 1 << '\n';
  return 0;
}