#include <fstream>
#include <queue>
#include <stack>

#define NMAX 100000

using namespace std;

int n, m, s;
int viz[NMAX + 1];

struct node{
    int inf;
    node* next;
} *G[NMAX + 1];

void add(int list, int x){
    node *p = new node;
    p->inf = x;
    p->next = G[list];
    G[list] = p;
}

void bfs(int s, int cc){
    stack<int> q;
    int x;
    q.push(s);
    viz[s] = cc;
    while(!q.empty()){
        x = q.top();
        q.pop();
        for(node *p = G[x]; p; p = p->next){
            if(!viz[p->inf]){
                q.push(p->inf);
                viz[p->inf] = viz[x];
            }
        }
    }
}

int main()
{
    ifstream f("dfs.in");
    ofstream g("dfs.out");
    f >> n >> m;
    int i, x, y;
    for(i = 0; i < m; ++i){
        f >> x >> y;
        add(x, y);
        //add(y, x);
    }
    int cc = 0;
    for(i = 1; i <= n; i++)
        if(!viz[i])
            bfs(i, ++cc);
    /*
    for(i = 1; i <= n; ++i)
        g << viz[i] - 1 << " ";
        */
    g << cc << "\n";
    f.close();
    g.close();
    return 0;
}