# include <cstdio>
# include <vector>
# define Nmax 100001
using namespace std;
vector<int> a[Nmax];
int n,m,x,y,nr,viz[Nmax];
void dfs(int p)
{int q;
 viz[p]=1;
 for(int i=0; i<a[p].size(); ++i ) 
	 {q=a[p][i];
	  if(!viz[q]) dfs(q);
	 }
}
int main()
{freopen ("dfs.in", "r", stdin); freopen ("dfs.out", "w", stdout);
 scanf ("%d%d", &n, &m);
 for(int i = 1; i <= m; ++i) {scanf ("%d %d", &x, &y); a[x].push_back(y);}
 for(int i=1; i<=n; ++i ) 
	 {if(!viz[i]) 
		  {nr++; dfs(i);}
	 }
 printf("%ld\n",nr); return 0;
}