#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
#define rep(i, a, b) for(ll i = a; i < b; ++i)
#define rrep(i, a, b) for(ll i = a; i >= b; --i)
constexpr ll inf = 4e18;
struct SetupIO {
    SetupIO() {
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout << fixed << setprecision(30);
    }
} setup_io;
struct UnionFind {
    UnionFind(int N)
        : n(N), data(N, -1) {}
    int merge(int a, int b) {
        assert(0 <= a and a < n);
        assert(0 <= b and b < n);
        int x = leader(a), y = leader(b);
        if(x == y) return x;
        if(-data[x] < -data[y]) swap(x, y);
        data[x] += data[y];
        data[y] = x;
        return x;
    }
    bool same(int a, int b) {
        assert(0 <= a and a < n);
        assert(0 <= b and b < n);
        return leader(a) == leader(b);
    }
    int leader(int a) {
        assert(0 <= a and a < n);
        if(data[a] < 0) return a;
        return data[a] = leader(data[a]);
    }
    int size(int a) {
        assert(0 <= a and a < n);
        return -data[leader(a)];
    }
    vector<vector<int>> groups() {
        vector<int> leader_buf(n), group_size(n);
        for(int i = 0; i < n; ++i) {
            leader_buf[i] = leader(i);
            ++group_size[leader_buf[i]];
        }
        vector<vector<int>> result(n);
        for(int i = 0; i < n; ++i) {
            result[i].reserve(group_size[i]);
        }
        for(int i = 0; i < n; ++i) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(remove_if(result.begin(), result.end(), [&](const vector<int>& v) { return v.empty(); }), result.end());
        return result;
    }

   private:
    int n;
    vector<int> data;
};
int main(void) {
    int n, m;
    cin >> n >> m;
    UnionFind uf(n);
    vector<int> in_deg(n), out_deg(n);
    rep(i, 0, m) {
        int u, v;
        cin >> u >> v;
        u--;
        v--;
        uf.merge(u, v);
        in_deg[v]++;
        out_deg[u]++;
    }
    vector<vector<int>> group = uf.groups();
    int ans = 0;
    bool flag = false;
    for(const vector<int>& v : group) {
        if(in_deg[v[0]] > 0 or out_deg[v[0]] > 0) {
            if(flag) {
                ans++;
            } else {
                flag = true;
            }
        }
        int cnt = 0;
        for(const int x : v) {
            cnt += abs(in_deg[x] - out_deg[x]);
        }
        if(cnt >= 4) ans += (cnt - 2) / 2;
    }
    cout << ans << '\n';
}