#include <fstream>

using namespace std;
const int N=100001;
const int M=200001;
ifstream in ("dfs.in");
ofstream out ("dfs.out");
int n,m,nr,vf[2*M],urm[2*M],lst[N];
bool viz[N];

void adauga(int x,int y)
{
    nr++;
    vf[nr]=y;
    urm[nr]=lst[x];
    lst[x]=nr;
}

void dfs(int x)
{
    viz[x]=true;
    int p=lst[x],y;
    while (p)
    {
        y=vf[p];
        if (!viz[y])
            dfs(y);
        p=urm[p];
    }
}
int main()
{
    in>>n>>m;
    int cnt=0;
    for (int i=1;i<=m;i++)
    {
        int x,y;
        in>>x>>y;
        adauga(x,y);
    }
    for (int i=1;i<=n;i++)
        if (!viz[i])
            dfs(i), cnt++;
    out<<cnt;
    return 0;
}