#include <fstream>
#include <vector>
#include <algorithm>
#include <deque>

#define MOD 4001

using namespace std;

ifstream cin("dfs.in");
ofstream cout("dfs.out");

vector<int> m[100009] ;

int d[100009] ;

void fil(int nod)
{
    if(d[nod])return ;

    d[nod] = 1 ;

    ///cout << nod << " " ;

    for(int f = 0 ; f < m[nod].size() ; f ++)
        fil(m[nod][f]) ;
}

int main()
{
    int n, q, s ;

    cin >> n >> q ;

    while(q --)
    {
        int a, b ;

        cin >> a >> b ;

        m[a].push_back(b) ;
    }

    int rez = 0 ;

    for(int f = 1 ; f <= n ; f ++)
        if(!d[f])fil(f), rez ++ ;

    cout << rez ;

    return 0 ;
}