#include <iostream>
#include <fstream>
#include <vector>
#define DIM 100005

using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

struct node{
    int val;
    node * next;
}*L[DIM];

int n,m;
bool used[DIM];

void add(int x, int y){
    node *p = new node;
    p->val = y;
    p->next = L[x];
    L[x] = p;
}

void citire(){
    f>>n>>m;
    int x,y;
    for(int i=1; i<=m; i++){
        f>>x>>y;
        add(x,y);
    }
}

void DFS(int i){
    used[i] = 1;
    for(node *p = L[i]; p; p = p->next)
        if(used[p->val] == 0)
            DFS(p->val);
}

int parcurgere(){
    int s=0;
    for(int i=1; i<=n; i++)
       if(used[i] == 0)
       {
           DFS(i); s++;
       }
    return s;
}

int main() {
    citire();
    g<<parcurgere();
}