#include <fstream>
#include <queue>
#include <stdlib.h>
#include <vector>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int main()
{
    int n ,m ,s = 0, i, x, y, j;
    int  *minim;
    vector <int>arce[100005];
    queue <int> pq;
    fin >> n >> m;
    minim = (int *) calloc(n, sizeof(int));
    for( i =0; i <m; i++)
    {
        fin >> x >> y;
        if (x!=y)
        arce[x-1].push_back(y-1);
    }
    for(j = 0; j < n; j++)
        if(minim[j] == 0)
            {
                s++;
                pq.push(j);
                minim[j] =s;
    while(!pq.empty())
    {
        x = pq.front();
        pq.pop();

        for(i = 0; i < arce[x].size(); i++)
        {
            y = arce[x][i];
            if(minim[y] == 0)
            {
                minim[y] = s;
                pq.push(y);
            }
        }
    }
            }
            fout << s;
    return 0;
}