#include<cstdio>
#include<vector>
using namespace std;
vector <int>v[100005];
int viz[100005];
int n,m;
void DFS(int nod)
{
    vector <int>::iterator it;
    for (it=v[nod].begin();it!=v[nod].end();++it)
    {
        if (viz[*it]==0)
        {
            viz[*it]=1;
            DFS(*it);
        }
    }
}
int main()
{
    int i,nr=0;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d%d",&n,&m);
    int x,y;
    for (i=1;i<=m;++i)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
    }
    for (i=1;i<=n;++i)
    {
        if (viz[i]==0)
        {
            ++nr;
            DFS(i);
        }
    }
    printf("%d\n",nr);
    return 0;
}