#include <stdio.h>
#include<vector>
#define nmax 100002
using namespace std;
vector <int> G[nmax];
bool use[nmax];
int n,m,s;
void DFS(int nod)
{
    vector <int>::iterator it;
    use[nod]=1;
    for(it=G[nod].begin();it!=G[nod].end();it++)
    {
        if(!use[*it])
            DFS(*it);
    }
}
int main()
{
    int i,x,y;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(i=0;i<m;i++)
    {
        scanf("%d %d",&x,&y);
        G[x].push_back(y);
    }
    for(i=1;i<=n;i++)
    {
        if(!use[i])
        {
            DFS(i);
            s++;
        }
    }
    printf("%d\n",s);
    return 0;
}