#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <bitset>
#define NMAX 100008

using namespace std;

int n, m;
vector<int> v[NMAX];
bitset<NMAX> viz;

void read(){

   int x, y;
   scanf("%d %d\n", &n, &m);
   for (int i = 0; i < m; i++){
      scanf("%d %d\n", &x, &y);
      v[x].push_back(y);
   }

}

void dfs(int i){

   viz[i] = 1;
   for (vector<int>::iterator it = v[i].begin(); it!=v[i].end(); it++){
      if (!viz[*it]){
         dfs(*it);
      }
   }

}

int main()
{
   freopen("dfs.in", "r", stdin);
   freopen("dfs.out", "w", stdout);
   read();
   int nrComp = 0;
   for (int i = 1; i<=n; i++){
      if (!viz[i]){
         nrComp++;
         dfs(i);
      }
   }
   printf("%d\n", nrComp);

   return 0;
}