#include <iostream>
#include <cstdio>
#include <vector>

const int MAX=100007;

using namespace std;

#define pb push_back
vector <int> gr[MAX];
int viz[MAX];

void dfs(int nod)
{
    viz[nod] = 1 ;
    for ( auto x : gr[nod] )
            if ( viz[x] == 0 )
                    dfs(x);

}
int main()
{
    freopen ("dfs.in" , "r" , stdin );
    freopen ("dfs.out" , "w" , stdout );
    int n , m  ;
    scanf ("%d %d" , &n , &m );
    for ( int i = 1 ; i <=m ; ++i )
    {
        int x , y ;
        scanf ("%d %d" , &x ,&y );
        gr[x].pb( y );
    }
    int sol=0;
    for ( int i = 1 ; i <= n ; ++i )
            {
                if ( viz[i] == 0 )
                    {
                    dfs(i);
                    ++sol;
                    }
            }
    printf ("%d" , sol );
    return 0;
}