#include <iostream>
#include <fstream>

using namespace std;

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

const int N = 1000001, M = 2000001;
int nr, vf[2 * M], urm[2 * M], lst[N], n, cnt = 0;
bool viz[N];

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

void dfs(int x)
{
    viz[x] = true;
    for(int p = lst[x]; p != 0; p = urm[p]){
        int y = vf[p];
        if(!viz[y]){
            dfs(y);
        }
    }
    cnt++;
}

int main()
{
    int i = 0;
    int v, m;
    in >> v >> m;
    for(int i = 0; i < m; i++){
        int x, y;
        in >> x >> y;
        adauga(x, y);
    }

    for(int i = 0; i < m; i++){
        if(viz[vf[i]] != true){
            dfs(vf[i]);
        }
    }

    out << cnt;

    return 0;
}