#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("dfs.in");
ofstream fout ("dfs.out");

struct nod
{
    int y;
    nod* next;
}*a[100005];

int componenta[100005];

void dfs(int idnod,int idcomp)
{
    componenta[idnod]=idcomp;
    nod* i=a[idnod];
    while(i!=NULL)
    {
        if (componenta[i->y]==0)
            dfs(i->y,idcomp);
        i=i->next;
    }
}

int main()
{
    int n,m;
    fin>>n>>m;
    for (int i=0; i<m; i++)
    {
        int x,y;
        fin>>x>>y;
        nod* nou=new nod;
        nou->y=y;
        nou->next=a[x];
        a[x]=nou;
    }
    int nr=1;
    for (int i=1; i<=n; i++)
        if (componenta[i]==0)
        {
            dfs(i,nr);
            nr++;
        }
    fout<<nr-1;
    return 0;
}