Mr. Kitayuta's Technology cf - 506B

//cf - 506B

const int N = 1e5 + 100;

vector<int> g_bi[N], g_uni[N];

int col[N];
bool cycle_found;
set<int> visited;
int comp = 0;
vector<int> node;
bool find_cycle;
int ache[N];

void cycle(int u) {
    if(find_cycle) return;
    col[u] = 1;
    for(int v : g_uni[u]) {
        if(col[v] == 1) {
            find_cycle = true;
            return;
        }
        if(col[v] == 0) cycle(v);
        if(find_cycle) return;
    }
    col[u] = 2;
}

int vis[N];

void dfs(int u) {
    vis[u] = comp;
    node.push_back(u);
    for(int v : g_bi[u]) {
        if(vis[v]==0) dfs(v);
    }
}


int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int u, v;
        cin >> u >> v;
        g_uni[u].push_back(v);
        g_bi[u].push_back(v);
        g_bi[v].push_back(u);
        ache[u] = ache[v] = 1;
    }
    int ans = 0;
    for(int i = 1; i <= n; i++) {
        ans += ache[i];
    }
    for(int i = 1; i <= n; i++) {
        if(ache[i] && vis[i] == 0) {
            comp++;
            node.clear();
            dfs(i);
            ans--;
            find_cycle = false;
            for(int u : node) {
                if(col[u] == 0 && find_cycle != true) {
                    cycle(u);
                }
            }
            ans += find_cycle;
        }
    }
    cout << ans;
    return 0;
}